It is they will need to make the police not so bad.
Make it illegal for police to lie about their intentions and the facts of the case (although perhaps they should be permitted to hide some of the facts of the case (although they cannot hide what you are actually accused of, or anything like that, if they are actually arresting you (since otherwise they should have no authority to arrest anyone)), and anyone (whether police or not) should always be permitted to claim "I don't know").
If you lie (or make a mistake) to the police while you are being interrogated, that should not be illegal (although making a false police report (while you are not being interrogated) would still be illegal).
Furthermore, any claim they make that, if valid, would not authorize them to do what they are doing to you, makes what they are doing illegal in that instance. For example, if you ask them if they are police and they say they are not police then they have no authority to arrest you (although they can still make a citizen's arrest (for situations where that is permitted, so, not necessarily all of the things that the police might arrest you for), or to call some of the police other than themself (using the methods that ordinary people would use, not the ones reserved for police), etc.
This isn't even half of enough to fix the problems with police, but it is a start.