Working as a clearing agent

I have just engaged in seaport clearing agency insha Allah with the aim of observing Shariah and sunnah. But I'm faced with the following questions.

1. Short payment to the government custom duty is common. Is it allowed? Short payment is paying for HONDA 1999 instead of 2003. Majority are involved in this even the custom officers overlook this. Contracting the clearing out makes the case worse as they will hide the short payment.

2. Also in the clearing offices people pay some amount that are already normal things over there but are without receipt. Are we allowed to
pay such money when we don't have options and its already their system. eg vehicle examnation officer will not leave his office unless such amount is paid. No special treatment will be given for ones job except that its their norm.

3. Police on the way also ask for money even after you have correct papers. Can we give them money?