The iPhone can make use of a wide array of apps that can help you with nearly anything, including selling, trading, and buying secondhand items. You can even sell your iPhone with your iPhone (yo dawg). However, when you're dealing with cash, you probably should use some trustworthy apps, right? We've been hard at work finding a few that will get the job done right and ethically. We've dug up seven apps that will help you get rid of your old items and acquire pre-loved ones.