There are a lot of creative and amusing investment frauds in the world, but there is one great simple investment fraud, one original source from which all the others developed:
Why don't people do this all the time? Well, I mean, they do. It's a pretty popular fraud. But it is usually a fairly small-scale and labor-intensive fraud, because most investors who are at all sophisticated realize that the risk-free 15 percent return is itself a red flag. Real investments are risky or uncertain or at least illiquid; the proper response to a guaranteed liquid 15 percent return is "what's the catch?"