[jacquesm]

> So your goal should be to keep things amicable and give them "an out" so they don't have to interrogate you.

That's key, and it is basic psychology.

Make sure the police officer has no reason to suspect you are hiding something and you'll get off without a problem, he/she hates wasting their time as much as you do.

Give a reason for suspicion or antagonize them and you're going to be a lot further in your day before you are let off.

A police officer is someone that has a relatively good eye for probability, if you are 'probably ok' (in other words, you're on the same side of the law) then there is no reason to detain you any longer and you can go. If you give them the feeling you are on opposite sides of that line (antagonistic behaviour for instance) then you may just have lost a couple of hours.