Benford's law is surprisingly effective in detecting unnatural patterns in data; I believe the IRS relies heavily on it. Then, alert eyes at the payment end, and encuragement to low-level clerical staff to cooperate in implicating their bosses or be left holding the bag. This works better for white-collar crime, since the criminal higher-ups are that much less likely to successfully put out a hit on persons who informed against them, though sometimes not for lack of trying.