Apple have had the ability to trade in devices for a while through their website but now they're bringing the trade-in service to their stores.
You can now check the value of your old Apple device on the Apple site. Then head over to an Apple store and trade it in for a new device.
You most likely won't get as much if you were to sell it on eBay or anywhere else, but it saves the hassle and time of having to find a buyer for your old device.
After trying the service, I found Apple offering £220 for the iPhone 5 Black 16GB, while they're going on eBay for around £330.
So if you've got the patience of selling it through somewhere like eBay, you will be better off.