I've never heard of "scan marks" either, but Googling that + poker turned up
this page, advertising a cheat-at-poker e-book. Among the claims are that you can read other players cards online.
My question is this: if you're blatantly advertising a how-to-steal e-book, how can anyone trust that you're not just ripping them off completely? Anyone who orders this is getting what they deserve (I hope).