I've bought several guitars on e-bay, most recently an almost new Ricky 360/12, without any problems. Actually I've had one problem, but it didn't cost me any money and it wound up turning me on to this forum.
Last year I was the winning bidder for about $2000 on a guitar that turned out to be a fraudulent listing of the October 2002 COTM Dragon Magic. The whole auction smelled. I was ready to demand further proof of ownership before I sent any $. I never had to because, within 5 minutes of the auction closing, I received an email from Mica warning me that it was fraudulent.
Obviously one has to use common sense. Check out the seller's history, not only whether they have positive feedback, but also what type of items they have previously sold. I sometimes even check out the history of the people leaving the positive feedback. A couple of times I found what appeared to be fixed auctions and feedback between the same buyers and sellers.
A great place to learn about the way that people scam others on ebay is in the rants section of Ed Roman's site. But, if one is cautious and uses common sense, ebay can be an incredible source of instuments. It certainly has a far more interesting inventory, (at least to me) than my local Guitar-in-the-box-Center.
Second chance offers on guitars? BEWARE (And certainly email the original buyer to ask if and why they backed out).
Bill, tgo