Be sure and tip your plumber rather than depend on his own motivation to do good and honest work, and I can guarantee you that a plumber can make a much bigger difference than a waitress in what he delivers, in terms of “service”.
If the plumber expects a tip, in light of the fact that it is NOT a traditionally tipping business, he’s SOL.
So, that’s a nice straw man.
Would you care to try again?