Fifteen visits since 1999 and I've been pulled over probably 7 times. Most of the time the officer told me what I was doing wrong and sent me on my way. Three times a bribe was hinted about, only one time did I pay $10 - the guy was relentless. We argued for 30 minutes and he wasn't backing down (N.Laredo).
Posted speed limits in much of Mexico are crazy slow. I often see traffic moving at 60mph on roads posted at 60KPH. I strive to keep up with traffic - go too slow and you'll be suspicious to police looking for a frightened tourist.
As far as corruption goes - in California a speeding ticket can approach $1,000 in fines and surcharges - same with Ontario.