Once upon a time, becoming a prostitute was difficult.

In, say, 1992, you could risk your life as a streetwalker—if you lived near a street where one could walk provocatively and reasonably expect to find customers. You could make and place an ad for sexual services in your local alternative weekly, at least if you lived in a city—but the responses wouldn’t begin until well after said weekly was printed and distributed. Of course, there were brothels, massage parlors, agencies, and so on back then, even an escorts section of the yellow pages. But it wasn’t as if any 20-year-old with a flash of curiosity about sex work could within hours find a client or a pimp and go into business selling herself.

Which brings us to 2012, and Room 216 of a Holiday Inn, somewhere in New Jersey.

It’s early afternoon and a 23-year-old college student—she asked that we use the name Brittany—is sitting on the room’s leather couch, waiting for the first of the day’s three clients to arrive, talking to me about her job. Brittany is blonde, attractive but not beautiful, a native of a blue-collar town in Camden County, N.J.

In a few hours she’ll be counting out nearly two thousand dollars in cash, not including $300 one of the men, a new client, deposited in advance into her PayPal account.

“I feel like on TV, you see things like the escorts are all crackheads,” she tells me. “They do drugs. They have pimps. They were abused by their parents and they were strippers. Not all of that is true.”

She’s part of a group of prostitutes who some have called the profession’s silent majority: independent, part-time, doing it as a matter of choice after entering the business by placing their own ad on public classified sites, and often keeping the work private from friends and family.

“When you take the profile of Internet prostitutes versus street prostitutes, you find there’s more education, and that more work temporarily, then exit,” says Scott Cunningham, an economist at Baylor University who has studied the impact of the Internet on prostitution markets. “They also are significantly less likely to work for a pimp.”

Internet prostitutes even look different than street prostitutes, according to Cunningham. He found that when Craigslist first entered a new area—this was in the days when it still had its “erotic services” category—the body weight of the women advertising sex gradually shifted to, in his words, “a more athletic body type. It moves from less attractive to more attractive in the eyes of the john.”

While critics have charged classified sites with facilitating sex trafficking, for women like Brittany, who have freely chosen prostitution and whose clients freely choose them, the Internet has made the transactions fast, simple, and discreet. New research suggests it hasn’t merely moved online and indoors those who once worked the street, but done something more transformative: created a different sort of sex worker—more educated, younger—and a bigger market of women selling sexual services in the United States and men purchasing those services.

If fewer women found a path into prostitution in the pre-Internet era, the same held true for johns: there was simply no practical way for a man to compare the looks and prices of large numbers of escorts, anonymously contact them, and receive reliable information that a provider was, in fact, not working for the police. Craigslist changed that.

Until 2009, the hugely popular classifieds site offered sex ads, with no charge to post or read. There had always been sex ads on the Internet, in chat rooms or niche websites, but their presence on Craigslist was something like the difference between a brothel on a side street in the bad part of town and a brothel in the Mall of America. On a single day in 2007, The New York Times reports, nearly “9,000 listings were added to the site’s ‘Erotic Services’ category in the New York region alone.”

Craigslist didn’t just lower the barriers to entry for sex workers and clients—it all but eliminated them.

The rise of Craigslist has changed how sex is bought and sold in two important ways, says Cunningham, the Baylor economist. First, sex work for women between ages 20 and 40 has mostly shifted from an outdoor activity involving street walking to an indoor activity involving online solicitation and communication. Second, because is it much easier to buy and sell sex, there are simply more prostitutes, and clients, than there were before.

Pressure from law enforcement, elected officials, and human rights groups—largely focused around child prostitution and trafficking—effectively shamed Craigslist into dropping its erotic services listings in 2010. The vast, lucrative market for online prostitution ads was up for grabs—and the bulk of it ended up almost immediately migrating to Backpage.com, the nation’s second-biggest classified site after Craigslist.

Classified websites, much like auction-market websites, tend to form natural monopolies because buyers want to go to the site with the most sellers, and sellers want to advertise on the site with the most buyers. Hence eBay has no real competitors, and in most categories (as any newspaper veteran will tell you), neither does Craigslist.

Backpage now posts nearly 100,000 ads for escorts and body rubs per month, collecting more revenue in its top 23 markets than its nine closest competitors combined, according to the consulting firm AIM Group. But while the bulk of the business moved to Backpage, some of the listings that had appeared on Craigslist simply disappeared—strongly suggesting that Craigslist hadn’t merely picked up the listings that previously were in print or scattered around the Web, but had actually increased the size of the market.

The Backpage listings for escorts and body rubs—which account for a staggering 80% of all revenue generated by Internet sex ads, according to the AIM Group, are the site’s dominant source of revenue, and account for the bulk of its 3.5 million monthly visitors. That’s been a financial windfall for Village Voice Media, the otherwise struggling chain of cash-losing alt-weeklies that also owns the listings site, and has used its papers to aggressively defend Backpage.

More regular, and committed market players, tend to migrate to the Erotic Review. The site is sort of like Yelp; it posts, to an audience of 250,000 monthly users, customer reviews of sex workers. A major obstacle for men looking for a prostitute is the fear of being arrested or set up for a robbery, and a reviewed escort is unlikely to be a cop or a robber.

Much like marijuana markets in New York City, as prostitution has moved online and off the streets, the market among consenting adults has become a very low priority for law enforcement.

Even New York Times columnist Nicholas Kristof, who has written movingly about the women and girls who have been trafficked on Backpage, said of the women placing ads on the site without coercion, “they’re not my concern.”

Rachel Lloyd, the founder of GEMS-NY, a New York–based organization that helps former sex workers recover from sexual abuse and form lives outside the sex industry, sees it differently. She has been an outspoken critic of Backpage for continuing to publish sex ads, but has also criticized activists who, in her view, have exaggerated the sex trafficking problem on the site. For Lloyd, herself a former sex worker, the dichotomy in the public’s mind about sex ads—the ads for trafficked women and children are bad, the ads placed by adult women who aren’t coerced aren’t so bad—is itself problematic.

“Even if you think they’re adult women, their stories aren’t much better than my 17-year-olds’. They’re just older,” Lloyd says. “In the last week I’ve had calls out for women, one 18 and one 19 ... They both had incredible trauma on their bodies from the experiences they had with johns. They aren’t 12, but they’re teenagers still.”

Brittany’s story illustrates some of the ambiguities of “noncoerced” sexual commerce. Sitting in the Holiday Inn, she talks about how she got started.

Her career began three years ago, when she was up one night, scanning the ads on Craigslist. She was 20 and living with her mother, working and going to school part-time. She clicked on the erotic services section, imagining that her money problems could be solved if she could find an older man looking to be her sugar daddy.

An ad caught her eye: it was from an escort agency, promising pay of two thousand dollars a week. She sent an email saying she was interested.

She met with the owners of the agency—two women, according to Brittany. They took photos of her and posted a listing on the escorts section of Backpage. A few days later, a male associate of the women drove Brittany to a hotel.

“I was forced to work from 12 in the afternoon to three in the morning,” Brittany says. “No breaks, no food, no anything ... I would sit in there. They would call and say ‘so-and-so is coming up.’ He’d come up. I would call and say he got there. Then when he was done I would call again and say he left. Then they’d say the next person’s coming up and I’d repeat that all day.”

Her cut was $100 an hour, half of what the women, who accused her of pocketing money, were charging customers. Brittney says she did well immediately, both because she was a new draw, and because the other women her bosses offered customers weren’t particularly attractive.

“It was really difficult to do because I hadn’t had sex with that many people in my personal life,” Brittany says. “It’s not something I thought I’d ever be doing.”

But she liked the money, she says, and it didn’t take long for her to realize that she didn’t need an agency to place a classified ad and rent a hotel room. She broke off contact with the two women, and went into business for herself, charging $300 per hour, advertising on Backpage as well as sites like the Erotic Review.

The days of 15-hour shifts were over; she’d book a hotel for six to eight days per month, from the afternoon till evening, with appointments lasting one or two hours. She hired a professional photographer to make her ads look more high-end. She limited her clients to, in her words, “older white men.” Her boyfriend of seven years, she says, believes she's a waitress in a strip bar.

“When guys come to the door they’re very polite,” says Brittany. “They’re very—they’re gentlemen. And if someone is not, I ask them to leave.”

To prove this point, Brittany says she’ll make an audio recording of the first few minutes with one of her clients. The man, who you can hear in the video accompanying this article, isn’t just polite—he makes every effort to impress her.

Client: This is an adventure. This should be fun.Brittany: Uh huh.Client: We should enjoy each other. This should be as much about you as it is about me.Brittany: I like that, yes.Client: Otherwise, it isn’t fun. It’s mechanical ... You know, if I want to go dinner—Brittany: Yeah—Client: If we want—if we want—to play at dinner, it becomes something we want to do.Brittany: And it’s totally fine, yeah.

When Brittany’s last client leaves, at 6:30 p.m., she can count her money: $1,800 in cash, plus the $300 waiting in her PayPal account.

Not so far away, on the streets of places like the Bronx, north Philadelphia, and Camden, there are streetwalkers soliciting customers—a vulnerable, and increasingly forgotten, class of sex worker.

But even part-time sex work with apparently harmless men can take its toll.

“I would honestly never recommend this to anyone,” Brittany says. “Girls, young girls, should find something else to do ... Like if my sister asked me about it, I’d be like: ‘No way. There’s no way you’re doing this.’”