I have been buying and selling electronics on ebay for about 10 years.
If you thoroughly read the description, you will be fine.
Ebay has to worry about its reputation. If a seller misrepresents an item, the buyer is eligable for a full refund.
Ask for pics
Do not do deals outside of the auction
Look at the sellers feedback, take a min to read some of the feedback
Pay with paypal
dont expect something for nothing.
I would avoid buying and selling out of the country.
With that said, I try my best to describe in detail. I learned my lesson years ago that "like new" for one person, might not mean the same thing to another. When I sell iphones, I also describe it as "shows signs of wear", even if it looks great.
You have to be careful with minor details in the description. There is a China version of the iphone out there. It looks just like our version, but it doesnt use the Apple OS and it doesnt work with itunes.
You can find a 3GS iphone for under $300
You can probably get ATT to sell you one for that price, you just have to renew your contract.