The financial fraud teams have models of what cash-based businesses 'should' look like. They don't, per se, care if these folks aren't paying taxes (the IRS does, and they have their own models). The Bank is looking more for things like "I'm a house cleaner...depositing $250k+ a year" (possible, but unlikely) or "I've been depositing 2-3k a month for a couple of years and suddenly I'm depositing 10-20k a month".