eBay uses a rating system for each seller/buyer. This tells you how many items they have sold and the feedback from the buyers. It is best to look for a seeker with a lot if feedback and positive ones at that. I could look at eBay for you, however I don't have personal knowledge of one that would be good for an iPhone. Have you looked in the marketplace here on Crackberry to see if anyone us selling one?
Posted from my CrackBerry at wapforums.crackberry.com