Generally speaking, you’ll get the most money when you sell your iPhone by selling it yourself—but you’ll also have the most hassles. Selling an iPhone via eBay or Craigslist will require you to deal with uploading photos and writing descriptions, plus addressing buyer inquiries, encountering possible scammers, figuring out shipping logistics, and more.
Instead of going the DIY sales route, most people resort to automated trade-in or sales programs offered by services with their carrier. They might not pay off quite as well as selling an iPhone yourself, but at least the payoff comes quickly and is relatively pain-free. The most effective way to get the most for your money with the least amount of hassle is to go through a third party buyback company. This is especially applicable if you are dealing with corporate cell phone recycling. Companies like BuyBack Solutions and a few others, deal mainly with corporate accounts when it comes to selling your iCloud bound devices like your iPhone and iPad.
When dealing in bulk devices like most companies do, these third party cell phone recycling companies can help out quite a bit. They deal with high volume buyback as well as electronic recycling and often times, data deletion so your secured data is always handled responsibly.