If you are being pulled over or is trying to pull you over by someone who you don't think is a LEO. Keep driving at a resonable speed. Head to some place public well lighted and with people around. If its a real LEO there soon well be marked crusiers joining in.
If you have a cell phone call 911 tell them that you are trying to be stopped by some one you don't belive is LEO and they soon well tell if is an official stop or not.
The key is to drive reasonably if it is a real LEO one doesn't want to be breaking a lot of traffic regulations.