Something to think about:
A couple of years ago, a collector who I am friendly with told me about someone who got in contact with him to see if they could work out a pretty big trade together (on-line). At one point, the guy forwarded him pics of things he had available for trade, some of which were actually downloaded/cropped/rearranged from
MY FRIEND'S own Flikr/ImageShack(?) account!!!! Upon seeing them he thought, "These cards look familiar," and checked the cert numbers to find they were indeed his! The pathetic scammer didn't even know that he was trying to scam the very guy whose bucket he raided!!! Right after that, my guy changed his account to private.
I guess the bottom line is, if someone says they have something to trade, make them send you a 'hostage video' where they are holding said cards with today's newspaper (if those exist anymore) to prove they got the goods.