FWIW ...

A plumbing contractor I know has a rather complicated accounting system ...

Apart from the base wage, there are bonuses for work developed, as well as several special accounts. One of these accounts is used to offset call-backs. Monies not 'spent' on call-backs are, at certain set points, paid to the worker.

There is a real need for the worker to have direct feedback on his performance. You can't improve without it.

Naturally, I would say that it's ONE call-back for a job ... if there's a second, it's time for management to get out from behind the desk, and go see what is really going on!