Let's say you are driving by and stop at light then someone in plain clothes puts a gun to your head and tells not to move. He says someone with your description just robbed a bank. He does not identify himself. He then instructs you to get out of the car and to put your hands behind your back. He put handcuffs on you. You demand to see ID, he refuses. He searches you and then he searches your vehicle. He finds nothing. He then apologizes and then let's you go.
You are lucky to be alive or not in jail. Had you resisted he could have shot you. If you did not allow him to search your vehicle, he could have arrested you and planted evidence and bring dogs that signal that you have contraband in the car. Or they bring dogs anyway trained to signal that you have contraband even though you are as innocent as Jesus, then they plant the evidence. And off to jail or spend 5 years in legal proceedings fighting the case. So one better be nice.