I've only been pulled over once, for speeding, and was let off with a warning. I've found that being cooperative, friendly, and immediately owning up to the offence you have committed helps you. Right away when I was pulled over, I apologized for speeding, didn't attempt to make any excuses, and had my license and registration ready. As I had a clean record, and was being very cooperative, the cop let me off with a warning. However, if the officer is having a bad day, or even doesn't like the way you look, you may be out of luck. They do not HAVE to let you off.