Or do the authors live under a rock? Idiots!
Walk into a donut shop or beauty salon run by the owner and pay with cash. Do you really think they’ll actually report that income to the IRS?
Small businesses advertise “cash discount” not because they wish to avoid credit card processing fees but because they don’t want to report the income!
Ironically the salaried middle class have somewhat fewer options for avoiding taxes, legally or illegally. They can’t take the bulk of their compensation as long term capital gains, nor are they paid in cash, and they lack possibilities for international accounting games.
You're stating gospel about conjecture. They're stating economics from mass statistics. Petty tax avoidance in the cash economy is understood and measured. Why do you think NBER are unaware of this?