I think there is always the off chance that the seller really doesn't know what he has, and it's the real thing. This Felix Mendolsohn Ruth looked real to me (although I can't be quite sure either). In the end the seller didn't know and ended the auction early to send the card it to get graded. (The listing was at $20 with 2 days to go when it ended). The ebay listing is here:
Link