I've bought hundreds of games off ebay and I only got scammed a couple times. When I do, I just report them and ebay gives a refund.
If it's risk of credit card reveal, that is the advantage of Paypal being the standard payment method. The seller doesn't get my card details.
(the only time I ever lost money on a game purchase was when I bought a Game Boy game off some some seller's own shopping site that used Google Checkout for payments. Found out Google, rather famously, had no customer service to report to for their service being used for fraud. Luckily I was only out like $10, for the lesson "don't use Google Checkout anymore.")
I just don't take a big risk on new sellers for valuable merchandise.
I'd also watch for HK/China/Russia sellers, places where bootlegs are known to be common.