Revealing mistake: When the cops bust the lab where the dope is cut they push a big man in a white T-shirt. The blood pack on his back is very noticeable.
Continuity mistake: When Bumpy enters the shop the amount of people outside changes at least three times.
Revealing mistake: When the man is set afire he is very obviously covered in fireproof gel.
Factual error: Early the movie, the maroon 1972 Monte Carlo at the intersection in the background is sporting wheels from a 1984 IROC Camaro Z28.
Factual error: As Lucas is leaving the bar to make a call to Saigon, a modern blue car passes outside, seen through the curtains. (01:51:55)
Answer: The idea is if cops wouldn't take a million dollars for themselves, free and clear without risk, they are impeccably honest. Therefore, they wouldn't accept bribes and probably not hold still for shakedowns or payoffs. They wouldn't cover up drug or weapon planting and would testify against crooked cops.