Mark

A mark is the fall guy, dupe, target, or victim in a scam. In other words, another carcass on the road to riches for the scammers, whether they be pseudoscientific or just plain criminals. In the TV show, The Real Hustle, presenter Paul Wilson uses the term in his pseudonym "Rob Marks" in reference to the fact he is robbing his marks.

A saying in poker goes, "If you look around the table and you can't figure out who the mark is, it's probably you."

Other (slightly more boring by our standards) uses

 * A common given name.
 * The title/author's name of one of the four biblical Gospels.
 * A sign or other distinguishing feature, whether real or abstract, such as The Mark of the Beast.
 * The pre-euro German currency.
 * A pro wrestling fan who believes it is real due to its nature of being presented as real when in reality the results are pre-determined, as opposed to fans who know that it's scripted (called smart marks or "smarks" for short).