I could think of a couple ways to churn a profit, albeit small, on ebay selling iphones.
1) Buy locked iphones, unlock them and relist them for up to a $50 profit potentially. most likely will only net you $20-$30 but if you're smart with your bidding and listing $50 is certainly possible.
2) Buy iphones with cracked screens, replace screen yourself using a kit and then relist them. Another potential $50 profit if you know what you're doing.