How exactly is it regressive? Do the higher income earners spend less money? Normally necessities of life (eg food) are excluded. There is also normally a credit for low income families.
15% of a Mercedes is a lot more than 15% of a used chevy!
The advantage is that reinvestment of assets is not taxed. The money goes where it will grow!
Its been awhile since my head was into the "Fair Tax" proposed. But, as I recall, the sales tax only applied to the first time a product was sold at retail... If still the same, then there would be no sales tax on the "used" Chevy.