[SolidSupplySide]

The NRST would also tax the underground economy - drug dealers have to buy ziploc bags, homeless bums have to buy clothes from somewhere

First of all, your examples are not the underground economy. When a drug dealer buys a Ziploc bag, SC Johnson and Co. along with its employees pays income tax on the sale.

A sales tax does not capture the underground economy. Noone pays tax on a drug transaction. Neither the drug seller nor the drug buyer.

[Poohbah]

A sales tax does not capture the underground economy. Noone pays tax on a drug transaction. Neither the drug seller nor the drug buyer.

When the drug seller pays for other goods, such as cars, clothes, et cetera, the proceeds of his transaction get taxed at that point.