Hey, let's incentivize cops to catch the bad guys! The salaries should depend upon performance. The more tickets and arrests, the greater income. Shirkers should be paid less - let's have them aggressively fight crime as if their income depended on it, and make their income depend on it.
Same for fire fighters; those who get to the fire first get paid, those who arrive late go out of business. I doubt anyone would sink so low as to start fires for greater income.