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.