Hi all,
lots of good advice in the posts. Another important move when a "hungry" official stops you for whatever reason - remove your keys from the ignition, put them in your pocket. Now it is not so easy for him to hold you to ransom.
Most times "I don't understand" enough times will work, but be really friendly even if they are not. Adopt a submissive body posture, and don't raise your voice.
If you really have done something stupid/illegal then it might be a good idea to negotiate, especially if there are witnesses and you have to be seen to be "punished", the cop doesn't want to loose face in front of the locals. You are travelling on, and are not so important to him, it's the locals that are his bread and butter.
Most countries have some degree of corruption among officials and law-enforcment, you just have to sense the situation. They will let you know that there is a problem, and how much they charge to fix it. If you have to fork over cash, especially in a border control area, do it discretly. Notes in a folded paper form, never in your documents. You can keep the price down by not going up the command chain - it's your choice whether you want to oil the system, but it's certainly not going to stop because you make a row.

Wishing all safe and troublefree travels

Peter, in Oslo