"so switch to a low flat tax and you'll eliminate a lot of tax evasion. I already see a lot of sales tax evasion in the real world as businesses hide the cash they receive from consumers."
-- in any type of income tax system, flat or progressive, the incentive, and the ease, of evasion is higher than it would be under an NRST:
Under the income tax, retailers only have to misstate sales just enough to wipe out sales profits in order to evade 100% of his tax bill. Under the FairTax, a retailer would have to hide all of his sales in order to evade 100% of his tax bill, which is simply not possible. Since the payoff for evading taxes is much smaller under the FairTax, the motivation to evade taxes is much lower under the FairTax.
if a retailer doesn't make any profit he'd still have to pay taxes?