This post originally appeared on Inc.

To show off the secret behind Pharma­packs, his $70 million retail business, Andrew Vagenas picked up an EOS lip balm and tossed it to his buddy Brad Tramunti. “Watch,” Vagenas said. “He’s like a special kid.” There is nothing about Tramunti that makes you think: lip-balm guy. He’s 33 years old and hefty, with a two-day scruff and a faded T-shirt wrapped around his torso. But he held the lip balm in his paw carefully, inspecting its lollipop-purple-swirl case like a savant.

“This is a new flavor,” he said. “Just came out. Blackberry nectar.” He took it to his desk and brought up its Amazon.com product page. He checked its weight—0.25 ounce. He pursed his lips and calculated the shipping cost in his head: “$1.89,” he muttered. He looked at its Amazon sales rank: 54,000. He brought up a page with suppliers’ prices. “We get this wholesale for $2.23,” he said, smiling. “That, plus shipping, plus our margin? We’ll be in the No. 1 spot.” That meant when a shopper clicked Add to Cart on Amazon, Pharmapacks would get the sale.

Vagenas grinned. Then he tossed Tramunti a box of Vitamin Friends Iron Diet Supplement. “He just gave me a crazy product right now,” Tramunti said. He pointed to his screen: The vitamins already had 201 Amazon reviews. “If we can get this for under 10 bucks, it’s a home run.” “We’re getting it for 11 bucks,” Vagenas said. “OK, it’s a double,” he shot back. “But we’re going to be No. 1 on this product—and it’s ranked 1,451 in all of personal care, No. 2 in vitamins. This is crazy! This is bonkers!” Whatever you want to call it, within hours, Pharmapacks would be the No. 1 seller on Amazon for both of those products—a ranking it would hold for weeks. “He’s my special boy,” beamed Vagenas.

The next time you buy some humdrum product on Amazon, pause for a moment and check the Other Sellers listed on the right side of the page. That lip balm? Thirteen vendors offer it. Those vitamins? Twenty. As you click and shop, a battle rages in that little box, fought every day by entrepreneurs like Vagenas and Tramunti on practically every one of Amazon’s 410 million product pages.

This is the Amazon Marketplace, where anybody can sell just about anything right alongside Amazon’s own wares. Unlike eBay, where each vendor maintains a separate listings page, Amazon tidily groups its Marketplace sellers by item, hiding away the inferior offers, to showcase the best deals up front. (In seller parlance, landing the No. 1 spot is called “getting the buy box.”) What looks so clean on your screen obscures the messy and massive jungle of the Marketplace: There are now more than 2 million sellers on Amazon. While the Seattle-based giant still sells the most popular items on the site itself, Marketplace sellers now ship nearly half of the products—about 2 billion items each year, all told—and those sales are growing twice as fast as Amazon’s, according to the consultancy ChannelAdvisor. The Marketplace started in 2000 selling used books. In 2016, it’s a retail phenomenon as significant as any in the past 50 years—together these sellers ring up what ChannelAdvisor estimates to be $132 billion in sales each year. That’s more than Walmart sold in 1997. Yet we know so little about who they are.

On 2015’s Inc. 500 list of America’s fastest-growing private companies, something stood out about the retailers. Nearly all of them, companies that were growing by 1,000 percent or more, had websites that looked a decade out of date. Like, a homepage. Maybe a few links to products. Why? That’s because, these days, such retailers don’t use their own sites much. They build their businesses on platforms—eBay, Walmart.com, Overstock, and especially Amazon.

Vagenas’s company, Pharmapacks, notched $31.5 million in revenue in 2014, which made its three-year growth rate 3,035 percent, good enough to earn it the 115th spot on the Inc. 500. By the end of 2015, its annual revenue was $70 million. Vagenas proudly told me the company was on track to do $140 million to $160 million in revenue in 2016, the vast majority coming from those platforms (and around 40 percent from Amazon). While other platform retailers have identified a niche opportunity and capitalized—search Amazon for horse brushes or pickle ball paddles and you can buy from two other Inc. 500 entrepreneurs—Pharmapacks sells everyday stuff found in drugstores: This upstart has succeeded by selling what most every retailer in the world, Amazon included, already offers. How?

Pharmapacks operates out of a low-slung warehouse in the College Point section of Queens, New York. From there, you can see the new World Trade Center, but otherwise the glitz of Manhattan might as well be a thousand miles away. Planes take off and land practically overhead. (LaGuardia Airport is across a nearby inlet.) The closest neighbor is a vast parking lot jammed with Time Warner Cable vans.

Pharmapacks’ warehouse has a different name on the sign out front. Tramunti got the door, and Vagenas was waiting behind his desk, a wary look on his face. He’s 34 and trim, and a slim gold chain was tucked beneath his plaid shirt. “I Googled your picture to make sure you were actually from Inc.,” he told me. Nothing personal, he said—but competitors always try to steal their secrets. One even sent a guy undercover to apply for a packing job, he added, staring at me for an extra beat. Then he cracked a smile.

Vagenas introduced me to his partners. Tramunti is an old buddy who grew up a few blocks from his house. Jimmy Mastronardi knows Tramunti and Vagenas from the neighborhood too. He once had a job in finance, so he’s the CFO. Two other guys, Jonathan Webb and his business partner, Adam Berkowitz, joined recently. They are older, in their 40s. The younger guys busted their chops about their age. But really, everybody was busting chops about everything. Constantly.

“We’re adding 4,000 makeup products, fragrances—” said Vagenas.

“And sex toys, I’m telling you!” Webb chimed in.

“Not under the Pharmapacks brand!”

“Call it Splash!”

“This guy—no shame,” Vagenas sighed, a thought bubble reading, See what I gotta deal with? But the company was considering it. “I always joke our bread and butter is anal cream,” Vagenas said. “Our top sellers are things nobody wants to buy at a store. But from there, people buy everything else.”

All the while, more than 100 workers, mostly women, stood at tables in the warehouse packing products into bubble-pack containers that looked like tiny space pods—Colgate toothpaste, Pantene shampoo. A man sat, an air gun in hand, inflating the containers nonstop. As soon as one crackled into shape, he grabbed the next, 15 times a minute. Psst-thwap. Psst-thwap.

Originally, Vagenas and Tramunti and another friend ran a pharmacy in the South Bronx. When they started selling health and beauty products online in 2011, they thought it could make a nifty side business. They rented a little warehouse on a leafy street six blocks from Vagenas’s childhood home in Whitestone, Queens, and started spending half the day there. Mastronardi soon joined them to help run the numbers. As they hammered out kinks, they discovered that selling on a platform like Amazon was totally different from running their drugstore or even a standalone website. It was also a much bigger opportunity.

You could fill a book with all the differences, of course, but the big one was: They could sell whatever they wanted, at whatever price, for whatever period of time. A Marketplace vendor doesn’t worry about stocking a full line of shampoos, or whether certain soaps are always on sale. If they want to sell lotion one week and hairspray the next, they can do that.

Early on, the guys decided that it would be easiest to offer whatever their suppliers had in stock. They built each online listing, and had a developer code a script that scraped the suppliers’ databases to enter each product’s information. When a customer ordered something, they in turn would order it from the supplier, pick it up, and then pack and ship it. That’s still the model, more or less, though nowadays they order in bulk using sales projections and need three trucks and a van to pick everything up. Inventory often stays in their warehouse only for a few hours before going right back out the door. The business is less like traditional merchandising than it is like a commodities trader from a bygone era, buying and selling well-known goods and turning a profit on each transaction.

Not that any of their family and friends knew the difference, at first. Their moms’ friends would call asking the Pharmapacks guys to pick stuff up for them. “I’m like, Listen! There’s a website!” said Vagenas. In the platform business, they learned, price is everything. Set a price too high, and Amazon buries it. Setting it too low is worse, earning the buy box and leading to thousands of orders flooding in—and a loss of money on every sale.

Vagenas, a problem solver at heart, loved turning Tramunti’s tricks into rules. He and the team had a developer code the tactics into algorithms, and baked them right into their proprietary software. Now the listings had optimal prices. Sales took off. They called the software the Master Brain. The Pharmapacks guys love the Master Brain. They protect it the way a star pit master guards the recipe for his barbecue’s rub. Or the way Pablo Escobar guarded the source of his ultrapure cocaine. Speaking of which: “You ever seen the movie Blow?” Tramunti asked me one day. He showed me the YouTube clip of the scene in which Johnny Depp, who plays the kingpin drug smuggler in the film, has his product tested by a black-market chemist—who goes gaga over its off-the-charts purity. “That’s us. We’ve got the Colombian cocaine of algorithms,” a proud Tramunti declared.

And as it did with Depp’s character in Blow, life got pretty crazy once the Master Brain’s pricing kicked in. Orders poured in. Sales increased sixfold in a year. Neighbors began complaining about the never-ending stream of UPS and postal trucks. They were also unhappy about the warehouse packers who, in the absence of a decent-size company cafeteria or nearby restaurants, plopped down on their lawns each day to eat lunch.

Other marketplace sellers have algorithms. There are now companies that design pricing software for platform vendors: ChannelAdvisor, WisePricer. But that’s all chump stuff when you have a Master Brain. “We can make listings in seconds,” Tramunti boasted. “Everybody else has to do all this hoopala hoppala.”

The conundrum fascinated Tramunti. He’d struggled with dyslexia in school, and like many with it, he’d developed an ability to memorize huge chunks of facts and figures to compensate—as he puts it, “we find workarounds.” He began studying all their products, memorizing competitors’ prices, watching as new items climbed the rankings. He toyed with different pricing strategies, figuring out formulas for how much they could charge for certain products and still get the sale. They started getting the buy box—and making money—more often.

Life as a Marketplace seller isn’t all algorithms and cash. Vendors also need high customer-service ratings to get the buy box. Keeping them that way is a grind, especially when you sell almost 25,000 different products and ship 570,000 orders a month. People get emotional about personal-care products. Including Vagenas’s mother, who called last summer to complain about her Coppertone suntan lotion. In July, it came with 10 percent extra. In August, it didn’t.”She was like, You basically robbed me,” Vagenas said. “I’m like, Mom! It was a promo!”

As Pharmapacks’ sales mushroomed, so did the complaints. Part of this was growing pains—it took a while to figure out how to fill so many orders fast without screwing up. But complainers are a naturally occurring species in e-commerce, and Pharmapacks now employs 16 customer-service reps, who field almost 200 concerns over the phone and by email every day. They write back to all customer inquiries within 24 hours—one of the key metrics Amazon tracks in its customer-service ratings. Two employees use a software program called Trustpilot to scroll through every 1-, 2-, and 3-star review the company receives and give each of them special attention. If a customer remains unsatisfied and won’t change the low mark, the reps appeal to Amazon’s Seller Support group—the judge, jury, and executioner in all customer-seller disputes—with detailed objections. Thanks to such micro-advocacy, Pharmapacks had more than 3,300 low ratings removed in 2015 alone. To put that into perspective, Pharmapacks products have been rated more than 280,000 times—and its Amazon rating is 4.9 stars.

But Vagenas’s desk is constantly cluttered with products that have caused problems. Each day, the Seller Support group takes down one or more Pharmapacks listings without warning because of customer complaints. One day it was a bottle of Dove Advanced Hair Series Quench Absolute Serum that was listed for fine hair but turned out to be for coarse hair. (The manufacturer changed the UPC code, Vagenas said.) Another day it was Cold-Eeze Cold Remedy lozenges. In each case, customer-service reps send Amazon copies of supplier invoices, product photos, and other documentation to get the item relisted, and Vagenas tries to identify the root of the problem and develop a protocol his staff can use to rapidly identify and solve similar problems in the future, so more products won’t end up on his desk. But every time I visited, some new toiletry had taken the place of the others on his desk. Uneasy lies the head that wears the crown of 4.9 stars.

Ever heard the phrase “It fell off the back of a truck”? No, not like that. Pharmapacks buys from the same established, law-abiding distributors that sell to national chains like Walmart, Costco, and CVS. But ask these distributors where they get the products, and some will give an answer as gruff and dismissive as the vehicular estrangement explanation above.

Pharmapacks has agreements with 16 suppliers. Some deal directly with manufacturers. Others get their goods in more circuitous ways. These tight-lipped suppliers are known by their critics as diverters. (They prefer “secondary market distributors.”) They acquire deeply discounted goods through gray-market methods, such as buying deodorant from a company that ordered too much. But diverters don’t discuss where they get their goods. Their lawyers will cheerfully tell you they don’t have to.

When people discuss the rise of online marketplaces, they tend to focus on the tech companies that have made it possible for shoppers to find and purchase things in a matter of clicks. But that explains only the demand side of the equation. It doesn’t explain the supply side—why all this product is available so cheaply and freely in the first place.

In 2014, a guy from Vagenas’s regular pickup basketball game asked to introduce him to a guy his girlfriend had met, Jonathan Webb. He ran a similar business, called StocknGo.Vagenas grudgingly agreed. “I’m thinking, I don’t know this fucking guy from a hole in the wall,” he said. “I didn’t want to bring him to the warehouse.” He brought Webb to a tiny offsite office where Mastronardi ran the numbers.

Webb, like Vagenas, has little patience for nonsense. “He was like, ‘What kind of shit is this?’” Vagenas remembered. “You guys doing $25 million out of this office?” Vagenas showed him a UPS statement so he could see exactly what kind it was: The shipper was processing 21,000 Pharma­packs orders a week. Webb and Vagenas connected right away. “Definitely don’t record this,” said Webb directly into my tape recorder. “But it was like love at first sight.”

“Weird as that sounds, he’s exactly right,” Vagenas said. Webb had barely driven away when Vagenas called his cell phone to propose they work together. Webb brought business and branding experience, since he’d previously run an ad agency. Webb also had a pertinent family connection. His wife’s uncle was the CEO of a distributor based in Ronkonkoma, New York, called Quality King, which is widely regarded as the largest and most successful diverter in the world.

As the tech companies have disrupted retail online, Quality King has spent the past few decades disrupting retail behind the scenes—on trucks, on freighter ships, and through good old-fashioned American litigation. Take, for instance, the 1998 Supreme Court case involving Quality King and a fancy shampoo maker named L’Anza Research. To preserve its cachet, L’Anza made its U.S. distributors sell only to exclusive boutiques and salons at high prices. But L’Anza sold its shampoo more cheaply in Europe, where it was less known. So several tons of L’Anza shampoo intended for distribution in Malta ultimately ended up on a ship headed for Ronkonkoma, for Quality King to sell wherever. (You could say it fell off the back of a boat.) L’Anza sued, claiming a Copyright Act violation, but the Supreme Court ruled unanimously for Quality King: A company buying products on the open market can resell them as it sees fit.

Quality King has been named in more than 50 lawsuits because of its business practices, four times under the RICO Act, the racketeering statute designed to bring down organized crime bosses. Time and again, Quality King walks away, no matter the circumstances. There was the freighter full of Paul Mitchell products that went all the way to China, where much was resold and loaded onto another ship heading to the Netherlands before ending up in Ronkonkoma. There was the con woman who promised to distribute various product samples on college campuses and elsewhere, but sold much of it to the University of Quality King instead. She went to prison; Quality King was untouched.

“Other tech companies—I’m not saying they don’t work hard,” sighs one founder, “but do you see what we have to deal with?” And courts continue to rule that, so long as the goods are authentic and the buyers come by them honestly, they can resell them as they please. One frustrated lawyer for brand owners, writing in a legal handbook, referred to the company as the “ever-innocent Quality King.” Precedents like these mean that if market­place sellers find a product for less, they can buy it, list it on Amazon, and get the buy box until they sell out, and there’s not much brands can do about it.

In June 2014, Webb and Vagenas teamed up, with Webb and Berkowitz taking an equity position in the company. Quality King is now a supplier, although Vagenas and Webb stress it is only one of Pharmapacks’ four major distributors and not its largest—it buys more from suppliers Kinray and H.D. Smith, for example. But it’s easy to see the influence. “We constantly get bombarded by manufacturers saying they want us to take their products off our websites,” said Webb. “Before I met these guys, they stopped selling products. They didn’t know any better. Now we have a team of attorneys.”

The same way the Pharmapacks guys won’t divulge the inner workings of their algorithm, they won’t tell manufacturers who their suppliers are, to keep them from snooping up the chain. “We don’t have to tell brands anything, and we don’t want to,” said Vagenas. “And, hypothetically, say a distributor cuts us off from a particular item. We’ll just go find it somewhere else,” said Webb. “You know who it works out for?” asked Vagenas. “The consumer. The consumer’s no longer getting gouged.”

“It’s Like Blood Diamond!” With all the pieces in place, Pharmapacks’ growth continues to skyrocket. Vagenas just signed a lease on a new, 142,000-square-foot headquarters. Late last year, the company installed robotics and conveyor belts to help package goods, and it can now prepare 50 orders per minute. They are in talks with the grocery-deliverer Fresh Direct, to sell and fulfill orders for health and beauty products on its site. The company is already doing the same for Walmart.com. It is also working with two of its distributors—naturally, Vagenas won’t say who—to bring a white-label version of its site to mom-and-pop brick-and-mortar drugstores, so that pharmacies like Vagenas and Tramunti’s old one in the Bronx can deliver goods as fast as the big guys. After growing up on Amazon’s platform, Pharmapacks is concentrating on its own.

Still, on a recent afternoon, Tramunti was hard at work, sifting through delisted items, checking and uploading each one using the Master Brain. “It’s tedious, it’s hard, it’s a real grind,” he said, checking boxes on his computer. “Other tech companies—I’m not saying they don’t work hard, but do you see the amount of shit we have to deal with? It’s not sexy. It’s like Blood Diamond! This is our Sierra Leone!” He cracked a wry smile, knowing, as always, that if he ever slips up, two million other sellers are out there, ready to do whatever they can to beat him to the buy box.

See also: The FBI v. Apple: What Does the Law Actually Say?