The problem with low level police corruption is, the common man has no one to turn to for justice. A bad cop, or two, can be reported, but when the organization is corrupt, there is nobody to help you except Zorro or the Mafia.
If someone robs you, there is no money left to get police action. And if the police do listen to your complaint, the thief has your money to bribe them with.
Living with this, on a daily basis, is more oppressive than reports of high level corruption, and probably the prime reason Mexico is mired in poverty.
