What to do when cops pull you over

I posted this in another thread but I got pulled over recently because my passenger (my son) was suspected (by the cop) of not wearing a seatbelt (which he was). I addressed the cop as 'officer' and explained that we both put on our seat belts before even starting the car (which was true). The cop questioned us for a few minutes while looking inside the car (I suspect he was looking for something). All the time I was respectful and kept both my hands on the steering wheel where he could see them. He had no proof and knew it and let us go.