On my own continent, North America, showing 'documentaçion' (paying a small bribe) is customary and not considered abnormal.
I enjoy spending time in Latin America and, truth be told, the system works. As a foreigner, I'm expected to pay more but the price isn't that much. If I were doing something illegal, I'd pay even more.
It doesn't even always have to be currency. Outside of the tourist areas, the policia may very well have a checkpoint before you enter a region. Cold beer is always welcome, as is soda. Etc...
That's right here on my continent. You can find that just driving outside the tourist areas of Mexico. There's some effort to make it look official, but you can hand them a magazine with $5 - $20 in it, and they will slip it into their pocket, flip through the magazine, and wave you through. If you use a porno magazine, they may just keep it.