The police normally have uniforms uncovered faces and come with warrants and badges which can be inspected verified and furthermore verified with dispatch if you call 911.

You could pretend to be an officer and people do but it would be easy to verify both at the time and after the fact making it a rarity because its hard to pull off.

Right now you could gather 3 bros and a van and snatch someone and it would probably take months to find out that they were murdered rather than in some holding facility or prison in El Salvador