The police depend on fear and intimidation to get what they want. Don't let them get away with more than they are allowed to because of fear. Cops are perhaps the most dangerous members of our society, so be careful when you talk to them. David Simon, a reporter for the Baltimore Sun in his book Homicide, pp. Simon reports that cops follow the letter of the law, ignoring the spirit.
Cops are tricky.
Ask for idenfication from any non-uniformed person purporting to be a law enforcement officer. If it really is police there will be more police cars appearing very shortly once you don't stop after the initial request to pull over. You should stop immediately at the appearance of additional police cars. If it is actually the police attempting to stop you, they will not be pleased that you didn't stop immediately, but they should understand your behavior and not hold it against you if you then deal with them correctly. Always keep your hands in plain sight and your arms at your sides when dealing with a police officer.