If you are stopped by the police, do your best not to hand over your original passport or driving licence. Carry several photocopies with you (you could need to show it for other reasons or other stops).

If you are stopped by a policeman pulling a scam they may tell you that you have committed numerous traffic offences which will result in heavy fines and possibly arrest unless you pay the officer at the scene. The amount owed is negotiable depending on how much cash (in any currency) you are carrying. 

If you hand them your original documents, they could be kept from you until you pay up.

If you cannot avoid this intimidating situation, at least you can keep your license and passport safe.