Check Points In Belize
Unlike in some other countries in the region where extorting tourists in rental cars is a small industry, in Belize you will usually not be pulled over for phony traffic offenses, and if you are stopped at a checkpoint, which often happens, it is rare but not unheard that you will be asked for a bribe.
If you are in a rental you are hardly ever harassed. Just make sure you have your driver's license available (you may also want to have a copy of your passport and other documents to show you are in the country legally).
Most police officers at check points are nice (once you are nice to them, of course).
Police normally check driver's license and your insurance sticker. That's about it. Almost always you will be on your way in seconds.
Of recent, the escalating crime in Belize means that rolling police checkpoints have increased.