Not a good comparison at all. Waitresses and waiters are often paid $3.00 or less an hour. Tips are their pay. Yes this is legal.
Plummers are paid $40.00 or more an hour. Big difference...
See post 16.
I know plumbers who don’t make your figure claimed, in fact where the company charges not much more than that, but who do you think can deliver great service or minimal service with the greatest range between those levels? Service plumbers doing hours of nasty, hard, dirty work in all weather and conditions out of your sight, or the gal bringing a plate to your table with you and her boss watching her?