I've bought 2 Cayman S's, 2 Audi TT roadsters, and a 370Z off of ebay. The Audis and the Z (bought for my sister) were all great cars, actually better than I expected. But my bids reflect the possibility of needing something repaired.
My burgundy Cayman S was bought from an individual in Houston. He forgot to mention the windshield was cracked in the auction. We negotiated a $400 discount and I was on my way.
The other Cayman S had a clean AutoCheck report (free on ebay). I didn't bother spending $35 on a CarFax because of that. Bad mistake as I found out after I bought it the CarFax mentioned a minor rear end incident. I also had trouble with the title on that Cayman - the seller sloppily wrote the mileage on the title and my DMV rejected it. The seller was a small used dealer in L.A. and getting another title from him was extremely difficult. I had several sleepless nights over that one. I don't know if it was my discussion with my state's Attorney's General or my discussion with the California DMV in LA, but someone got to him and he finally sent me a title.
BTW... I still have the 2010 Audi TT for sale. It's one of the nicest, cleanest cars I've ever bought. Inquire within if interested.