I've been thinking of buying an iPhone on eBay but just thought that I'd hate to pay market value for the phone and end up getting one that's maybe had its screen replaced with sub standard hardware. One thing that made me think of this is a friend had her iPad's screen replaced in the mall and weeks later noticed it wasn't sealed properly. I know this is different, especially with a 4S, but I'm a bit worried that I'll find an issue weeks or a month or two after the sale and it'll be too late to do anything. Any advice on how to prevent this? Other than not buying from eBay? Does this happen often? Is it a real concern?