From a Wall Street Journal books column by Katrina Gulliver headlined “‘Fool Me Once’ Review: Scam Filter”:

You know the saying: “You can’t cheat an honest man.” It assumes that those who are the target of a cheat asked for it. The investment fund with the suspiciously high returns, the inside racing tip, the stock trade that’s a “sure thing”—the investors knew, or should have known, that something was off. The victims thought they were in on the con, and it turned out they were the marks.