It's bad enough when traffic police stop people for actual infractions, and then accept bribes to let them off (this is common throughout South Africa). But when one starts hearing stories about perfectly law-abiding citizens being stopped and harassed for bribes (in more isolated municipalities), one gets really worried.
I'll could be accused of "Afro-pessimism", if I point this out, but I've been told that in Nigeria, you never stop for a police officer, because he'll try solicit a bribe.