Completion count is the metric everyone starts with and the one that teaches the wrong behavior. Callback rate is the honest one, and it is usually not measured at all.
Pay is the reason given at the exit interview. The reasons underneath are usually a whiteboard, a radio, and a supervisor buried in paperwork at the end of every shift.
A bonus on work orders closed teaches people to close work orders twice. Pair it with callback rate, cap the individual component, and put turn time on the whole team.
Closure rate says the ticket closed. Callback rate says whether the resident had to call back. One of those measures quality and it is not the first one.