iPhone 6 release could drive the most old iPhone trade-ins ever

As the iPhone 6 launch approaches, more trade-in sites are clamoring for your old iPhone. eBay is leading the charge with the promise of a $100 coupon if you can't sell yours on the auction site.

There's gold in them thar phones! CNET

It's widely believed that Apple will introduce the iPhone 6 at a September 9 media event in San Francisco, making it prime-time for trading in current and older Apple smartphones. Plenty of big and small online names are already jostling to offer the best deal to take your old iPhone off your hands, and now eBay is sweetening the pot even more.

A representative for eBay tells me that the auction site will be offering a $100 coupon to US sellers who are unable to sell their old iPhone between September 1 and October 24.

Currently, a used iPhone 5s can fetch $500 or more on eBay. The site notes that after the iPhone 5s and 5c became available last year, the average selling price for used iPhones (including the iPhone 4, iPhone 4s and iPhone 5) was around $280. eBay also says that the number of iPhone listings continues to increase with each new generation release.

Trade-in site NextWorth is also expecting to see a boom in its business with the release of the iPhone 6. The company anticipates double the trade-in volume in the coming weeks as compared to last year's launch of the iPhone 5s and 5c. Nextworth's historical data shows a 105 percent increase in trades when Apple introduces a brand new "numbered" model, versus the less dramatic changes that typically accompany an "s" version. (To be fair, the introduction of Siri in the iPhone 4s was perhaps a bigger deal than the iPhone 5).

Nextworth has a partnership with Target that allows people to trade in their old iPhones in exchange for a Target gift card. At the moment, you can hand over an old iPhone 5s in exchange for up to $259 so long as it's fully functional without a cracked screen., a kind of peer-to-peer hybrid of eBay and Nextworth (it helps facilitate price, shipping and money movements between individual buyers and sellers), also told me it has seen iPhone-related traffic more than double from last year's lead-up to the iPhone 5s and 5c launch.

If you're hoping to get the most for your old iPhone, there's no time like the present, especially this year with so many other used iPhones hitting the digital streets. Glyde currently suggests a sales price of $413 for a used Verizon 64GB iPhone 5s, which is down from a price of $487 the site was suggesting just a week ago.