[Brendan]

Whenever the seller says he knows nothing about his cards and/or card collecting.

"I don't know anything about these cards or how to get them graded but my grandfather left them for me when he passed away. The bidder can decide for himself whether these are real or not."

Anything along these lines is clearly going to be some sort of reprint.

High end ungraded cards are another thing you've got to watch out for, but can be trickier because they often are real. Less feedback is important, too. I usually like to check the actual comments in his feedback because a lot of these guys aren't good buyers and that often translates to a bad seller.