first of all, you should increase cop's income.
not the income you get every few minutes, but the one that you gets from bad citizens.
considering how robbers can make 100~200 golds in few secs by killing dozen citizens, cops have to wait for 5 seconds to
have a CHANCE to search citizens. I see that you used different money item for bad citizen(money bag) and good citizen(paper money). Thus i think you can manage that. Also, i suggest you should gradually increase police upgrade costs, say 2 golds per each upgrades. When there's someone who knows how to play the game, at about mid game, the police upgrades are kinda ridiculous. something like 20 weapons upgrades with booster jets up their butts (not literal)
. Another thing is money you get from chop shop. 10-20 minerals per car sounds too cheap considering it has 40 secs delay, not to mention you can earn same amount of money by killing only 1 or 2 citizens. After all, it is a car you are selling. I'm sure they cost more than amount of money you carry in your wallet.
ps. congratz for getting into top rated! good work.