If where you are is a deciding factor as to whether or not you can trust the police, then the safest measure you can take is to simply not trust the police.
Even if some precincts may be more trustworthy, the overall nationwide result of how police act, is that the left gets free passes, and the right gets the book thrown at them.
This goes beyond police to include pretty much the entire law enforcement and justice system. While the lefties on the street night fight it, this is just another institution that's been taken over from the inside by leftists. Just like the education system, the media, a good portion of corporate America, big tech, etc.
Some different locales may vary, but the overall result is that the system gives an advantage to the left.