Seriously? Are you really being serious?
The amount of tax avoided by contractors is far greater than the amounts we are talking about with the rich and famous. Tax evasion at the lower level is rife, and illegal, and all too often left unpunished.
So in a perfect world where all the tax was collected correctly from EVERYONE that was due to pay it, yes, I do think it improbable that a builder would do less cash in hand, and mainly because customers wouldn't have it.