Law enforcement officers seeking bribes is rare in my experience. I've been stopped five times in Mexico and 3 times the officers tried to squeeze money out of me. One time I paid $20 after 45 minutes - another time a National came to my defense and argued with the officer who relented. The third time I was able to get the officer to give up and let me go.
It's the culture there. Compared to $500 speeding tickets (in the US) with associated surcharges and points, Mexico is a motorist's bargain if you can get out of a ticket for $20.
If you notice how Nationals drive in Mexico, traffic enforcement is pretty laid back compared to the US.
Have fun! My advice is that you'll probably have a better time on your own.
