eBay is definitely going to be your most secure method of selling ANY used item. There are websites like "Gazelle" that offer to purchase your used smartphones. However, the price you'll get from them is well below the market value for a used, good condition device. I'd go w/ eBay, though. Yes, you're going to pay a small listing fee and/or % of the final sale price. More than worth it for the security.
Agreed. You can try swappa. They have started listing iPhones as well. Its primarily a place for android. It's free to list with a flat fee of $10 when you sell. And you can buy trade or organize a swap as well.
"Be nice to people on your way up because you'll meet them on your way down." - Wilson Mizner