This doesn't work in some fraud cases. If Madoff is selling you an investment, it is obvious what you think he gets out of it, he invests your money and keeps a

This doesn't work in some fraud cases. If Madoff is selling you an investment, it is obvious what you think he gets out of it, he invests your money and keeps a proportion and that is normal business right? As the article says, his clever angle was not to over-inflate the ROI of the investments which might well make them look implausible. What is harder to spot is whether an investment is actually taking place.