Does Canada have a sales tax?
Exactly. Even though they are payed with cash, they purchase goods and pay State & Local Sales Taxes. In D.C., the Sales Tax is 10%, in NYC, 8.25%.
Whether we want to admit it or not, I'm sure every business owner in this forum wouldn't hesitate to take $20.00 from an illegal immigrant that wants to purchase their goods regardless of their political opinion about immigration.
This country has always have & will continue to depend on cheap labor, just keep better track of them via an amnesty program (like Bush wanted in his first term).