To find out where you can expect the best return on your dollar, we bought an iPhone from each reseller service and then turned around and re-sold that phone to same service where it came from. We also rated each service on their convenience, ease of use and responsiveness to come up with our rankings.

The key takeaways from our testing:

Glyde and Swappa top our rankings of the best places to buy and sell a used phone.

Walmart and Best Buy finished at the bottom.

We resold our iPhones for an average of 52 percent of what we had paid for them.

We got the highest rate of return from marketplace services that connect smartphone buyers with sellers; the worst return came from big-box retailers.

How we tested

To best measure how much return you can expect from iPhone resellers, we selected services that both buy and sell used iPhones, evaluating seven. In addition to Glyde and Swappa, we also looked at Amazon, Best Buy, GameStop, Gazelle and Walmart. We bought a used iPhone from each service, and then — without activating or using our newly purchased phone — sold the same model back to the seller where we purchased it.

From most resellers, we bought a 16GB iPhone 6. We purchased a 16GB iPhone 6 Plus from Amazon and GameStop due to availability issues, though we stuck with iPhones released in 2014 to get comparable quotes from resellers. Also, due to availability, some of the iPhones we purchased were tied to specific carriers, which we've noted below. In our experience, unlocked phones not tied to any one carrier generally fetch higher prices (though AT&T and Verizon phones have a high resale value, too).

As you might expect, there's a gap between what resellers will charge you for an iPhone and what they're willing to pay out when you try selling that same phone back. Just like with cars that depreciate the moment you drive them off the lot, that iPhone you're hoping to unload will never recoup its value. In our testing, resellers make their money by buying low and selling high.

When ranking these seven services, in addition to measuring how much we got back when reselling an iPhone, we also took the entire process into account. Were the instructions easy to follow? How quickly did it take to get a quote on our iPhone? Did the reseller offer cash or store credit? And how promptly did we receive that cash or credit after completing the sale?

Glyde: Our top pick

What we bought: Space Gray iPhone 6 (AT&T)

What we paid: $359.50

What we got back: $265.60

Rate of return: 74 percent

Cash or credit: Cash and bitcoin

Pros: Best rate of return; Clear explanation of policies with explicit breakdown of fees; Option to wait for a better price; Can verify your identity via PayPal; Flexible payment options

Cons: You're not required to post a verification photo, a step that can help weed out scammers.

Glyde offers a straightforward, colorful and easy-to-navigate website where you can find an assortment of second-hand iPhones as well as Android models from Samsung, HTC, LG and others. To sell my iPhone 6, all I needed to do was select the website's Sell tab and type in the phone's model number, carrier, color and condition. Several questions from Glyde covered details about physical appearance and scratches, personalization, and whether I had included accessories like a power adapter and cable.

Note that prices can change, often from day to day. After trying a dry run, I went back to Glyde to re-enter information about the phone I was trying to sell, and the market price had dropped to $316 from $326.

The market price is what the buyer is going to pay, not the amount I would pocket. Glyde charges a 15-percent transaction fee, while a kit with packaging to ship off your phone will cost you $3. Glyde was the most transparent service when it came to spelling out fees. I wound up collecting $265.60. (That amount would have been $274.10 if I had stuck with the quote from my dry run.) That's still the highest percentage of return from any vendor we tested, as we got back 74 percent of what we paid for the iPhone.

While I was disappointed with the price drop over two days, I decided to take my profit immediately and hit the List for Sale button. From there, you type in information about the phone, enter your email and Glyde account password, and verify your identity with your credit card or PayPal account. Click the button, and your item is listed. You can post your listing on Facebook, Twitter and Google + right from Glyde's page.

Two days after I listed my phone for sale, a buyer bit and then reneged within an hour; Glyde notified me via email about both events. The next day, another person offered to buy, which I quickly confirmed. A packing box arrived in the mail, with a prepaid label; all I had to do was drop the package into the nearest mailbox. Three days after the buyer receives and accepts the phone, Glyde posts the money into your account. From there, you can transfer the cash to your bank account, opt for Bitcoin payment or have a check mailed to you for a $2 fee.

Swappa: Runner-Up

What we bought: Space Gray iPhone 6 (Verizon)

What we paid: $465

What we got back: $325

Rate of return: 70 percent

Cash or credit: Cash

Pros: Posted items are approved quickly by Swappa; Ability to adjust listing; Solid rate of return; Added protection via PayPal purchases

Cons: Time-consuming process required for shooting photos of your phone; Agreeing to an immediate trade will lower your rate of return; Mandatory $10 PayPal transaction fee.

Swappa — as in "you wanna swappa?" — is an electronics website that features a fun interface for selling several dozen brands of phones, including Android devices as well as the iPhone. Just type in the specific search term to find the model you want to sell, and if it appears, you get an immediate idea of how much cash you'll get.

My Verizon-tied iPhone cost $465, and from the site's initial offer, I would have pocketed up to $307 in cash, which came to 66 percent of the total I paid for the device. Swappa also gave me the choice of selling my phone for from $340 to $559 if I wanted to wait for a better deal. I opted for a better return — and to take the deal, I had to register, either through Facebook or Google+ or via email and password.

It took longer to get my listing up on Swappa than it did with other sites. The process requires you to shoot a verification photo of the phone and its accessories using a specific, rather low-tech approach. You have to set up your shots with the site's verification number handwritten on a piece of paper next to the phone, and then powerup the phone you're reselling, so the screen is lit when you take your picture. You repeat the process with any included accessories. The idea is to prevent scams, and Swappa at least offers ample instruction on how to take your picture.

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After I took the photos, Swappa took 15 minutes to verify and approve my entry. From there, it's a matter of waiting for someone to buy your phone. If you've tried to get a higher price, you can revise your listing to Swappa's lower price, which I did after waiting three days. The phone sold only after I settled on a new price: $335, which netted me $325 once I took into account a mandatory PayPal transaction fee.

That PayPal fee is the only cost — there's no fee to sell on Swappa — and using PayPal to handle transactions felt safer than having to punch in credit card information. Swappa reviews and approves all listings before buyers can see them. Swappy promptly answered my questions about my listing when I sent queries via email and posted them to Swappa's Facebook page. When my phone sold, I was notified that money had been deposited in my PayPal account, after which I had two days to mail out the phone.

As an extra added layer of protection, anyone who sells a stolen phone, or one with a damaged screen or water damage violates Swappa's terms of use, giving buyers recourse through PayPal.

Gazelle

What we bought: Space Gray iPhone 6 (Verizon)

What we paid: $406

What we got back: $210

Rate of return: 52 percent

Cash or credit: Both

Pros: Quick and easy resale process; Multiple options for getting paid for your device; Inspection processensures quality selection of phones on sale.

Cons: Middle-of-the-road payment for trade-ins, compared to other resellers.

Gazelle has an attractive site that makes it easy to get started with your sale: The company trades in iPhones and Samsung Galaxy models as well as Android devices from HTC, Nokia, LG and others that cover the four major carriers.

If you take Gazelle's offer on your phone, you have a choice of payment via Amazon gift card (which adds an extra 5 percent to your total), PayPal, charitable donation or standard check delivered within 10 days of Gazelle verifying the phone's condition. Customers buy your phone from Gazelle, not you directly, and the company inspects the device before selling it as certified pre-owned to guarantee the condition. To ensure buyers are satisfied, there is a 30-day return policy.

After you enter your email address and a minimum amount of information about the phone's brand, capacity and physical condition, you do not have to wait for a buyer — just accept the Gazelle offer, box up the phone and choose how you want to be paid.

As a reseller, Gazelle will appeal most if you want to unload your phone quickly and would like some options for how you'll be reimbursed. We got back only half of the value of the iPhone we had bought, though.

Amazon

What we bought: Space Gray iPhone 6 Plus (unlocked)

What we paid: $549.99

What we got back: $265

Rate of return: 48 percent

Cash or credit: Amazon gift card

Pros: Process is clearly explained; Trade-in offer is immediate; Amazon offers free mailing label for sending in your phone.

Cons: Prices paid are fairly low; You're restricted to store credit; Trade-in links can be hard to find.

To sell your old smartphone on Amazon's massive website — which appears to sell a huge variety of almost every brand imaginable — requires an eagle eye and some clicking around to find the right path. In the end, typing the exact item into Amazon's search box, clicking on a result and finding the trade-in link on the page was the quickest way to get an estimate.



For an iPhone 6 Plus that we bought for $549.99 from the e-commerce giant, Amazon offered $265 in trade — less than half of what we paid. While your phone's appearance and condition may be acceptable to you, Amazon reserves the right to inspect the device and asks straightaway if you will accept a lower price or if you want the phone sent back if your price and Amazon's don't match. After my phone passed inspection, Amazon deposited the proceeds of my gift card directly into my account.



The company's trade-in program offers an Amazon gift card in exchange for your used phone. If you don't mind registering as an Amazon seller — which involves entering credit card and tax info — you can sell your phone on Amazon's individual seller marketplace. But that's a lot of hoops to jump through for a one-time sale, especially when the gift card can be used to buy any of the hundreds of thousands of things Amazon sells on its site.

GameStop

What we bought: Space Gray iPhone 6 Plus (AT&T)

What we paid: $459.99

What we got back: $240

Rate of return: 52 percent

Cash or credit: Both

Pros: Choice between cash or store credit; Simple process; In-store staff were helpful and professional during our testing.

Cons: Middling return on the value of our phone; Requires a visit to a brick-and-mortar store to complete your sale.

GameStop takes a different approach than other resellers because of its focus on games. While some resellers offer a mix of cash and credit, GameStop customers may be more inclined to trade in their phones for store credit in games, VR headsets and gaming systems, in addition to the refurbished iPhones and Samsung Galaxy models available on the GameStop site. The transaction is straightforward except for one thing: The final turnover of your phone for cash or gift cards must be done in person.



The website offers a list of the phone types GameStop accepts for trade. A working iPhone 6 Plus that has no missing parts, cracks or dents will trade or get cash totaling $240. That's a little more than 52 percent of the $459.99 we had paid GameStop for the same phone the previous month. A damaged phone will trade for $95, while a dead phone gets $25.



My trade-in experience took just 15 minutes, as the pleasant and efficient clerk behind the counter tested the phone and looked up records. I walked out with a $240 gift card.

GameStop lets you search for stores within a 15-mile radius of your zip code. If there's no retail outlet near you, you'll want to turn to a different reseller.

Walmart

What we bought: Space Gray iPhone 6 (Straight Talk)

What we paid: $369

What we got back: $125

Rate of return: 34 percent

Cash or credit: Credit

Pros: Simple transaction requiring little information; Free shipping label supplied.

Cons: Very low return on resales; Limited to in-store credit.

You'll find plenty of phones available for sale at Walmart, including contract, unlocked and refurbished phones available for the major carriers as well as the retailer's in-house Straight Talk network. What you won't find is the option to get cash back for your phone. It's store credit and no negotiating.

It's easy enough to go through the process, using the Gadgets for Gift Cards link. The used iPhone 6 we bought from Walmart netted a $125 offer, 34 percent of what we paid, which was the lowest return from any reseller. Interestingly, the phone was tied to Straight Talk. Had we tried selling back an unlocked phone or one tied to AT&T or Verizon, Walmart would have given us $160 in credit.

Once you approve Walmart's appraisal, just log in to your account or create a new account with your email and mailing address. Walmart offers a printed label that you can use to pack up your phone and send it in. After that, just wait for your gift card to arrive via email, which it did within three days of receiving my phone.

Best Buy

What we bought: Space Gray iPhone 6 (AT&T)

What we paid: $599.99

What we got back: $208

Rate of return: 35 percent

Cash or credit: Gift Card

Pros: Trade-in process is simple, if you have no questions; Trade-ins at the store are handled efficiently by friendly staff.

Cons: Long wait times for answering questions on Best Buy's 800-number; Low rate of return.

Best Buy has a busy website that features a vast variety of iPhones and flavors of Android phones for sale. But it's still fairly easy to find the place to trade in your older iPhone. If you do, be prepared to accept payment in credit. Like Walmart and Amazon, Best Buy doesn't deal in cash for phone trade-ins.

We paid $599.99 for an iPhone 6 that arrived in a sealed box (for an iPhone 6s oddly) but with no earbuds included, the only used phone we bought that was missing an item. That didn't affect my trade-in price; when I turned in my iPhone for resale, the Best Buy clerk said I didn't need to include accessories. But Best Buy's offer was the second-lowest return from any reseller: just a $208 gift card, or 35 percent of what we paid for the iPhone.

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Getting a quote from Best Buy's website is simple enough. All I had to do was list the phone's color, carrier and condition to get a trade-in value that I could redeem in person or by mail. Getting answers to questions proved more difficult. I called Best Buy's toll-free number to ask about the missing earbuds and an issue with the phone's IMEI number, and waited 20 minutes and through three transfers before I was told it would be a better idea to do my trade-in at a store. That took a much more efficient 15 minutes.

Other options

You don't necessarily need to go through a reseller or e-commerce marketplace to unload your aging iPhone. Certainly, Craigslist offers the opportunity to find a willing buyer, and depending on your negotiating skills, you may be able to get a bigger return than you would from a reseller who's going to offer you a set price.

That said, handling a sale on your own can be a hassle, and there's always the risk of running into scammers. A reseller or reputable marketplace removes a lot of the headaches and potential risks.



If you're planning on using the money you get from trading in your phone to finance the purchase of a new phone and you're committed to a specific wireless carrier, you may want to see what that carrier will offer you for your old phone. Verizon offered us the best quote on an iPhone 6, with a $265 trade-in value. AT&T quoted us a price of $200 for a 16GB iPhone 6, while T-Mobile and Sprint offered $191 and $159, respectively. Those quotes assume a phone is in excellent condition, and the amounts can vary based on which carrier your old phone is tied to. You receive the trade-in value in the form of credit or a gift card.

Where to buy a used phone

Our testing of reseller services focused primarily on selling a used iPhone, because that's where you're likely to experience the greatest amount of variance, from the money you get back for your phone to the simplicity of the resale process. In contrast, shopping for a used iPhone from these sites is a pretty similar experience, though there are a few differences worth noting.

In terms of selection, you'll generally find each service offers a wide degree of smartphone models and capacities. In our search for a used iPhone 6, we found that models tied to AT&T and Verizon were plentiful while T-Mobile and Sprint devices were in shorter supply. Amazon, Glyde and Swappa offered the widest range of phones in terms of carriers and capacities.

Used iPhone shoppers will find the best range of prices at Swappa, though lower-priced phones are likely to have been well-used. Glyde, Gazelle, GameStop and Amazon also offer attractive pricing on used phones depending on what model you're looking for.

We found it easiest to shop for a used iPhone at Glyde and Swappa, which conveniently group iPhone models together, allowing you to drill down to the version you want. Despite its wide selection, Amazon offers very cluttered search results; type in iPhone 6, and you're just as likely to get entries for the 6s, 6s Plus and 6 Plus as you are for the model you want. Walmart and Best Buy feature helpful filters for removing superfluous search results.

We should note that we ran into one quirk when buying our phones from Glyde and GameStop, though that's likely a result of how we ordered our iPhones. Because we bought our phones through our corporate office and shipped them to an editor at another location, both Glyde and GameStop flagged our initial purchases, requiring us to set up a PayPal account to complete the deals. Most shoppers won't run into that problem, though it could flare up if you're buying a used phone as a gift for someone who has a different address than yours.

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