We recently found out that there is a system in place that we didn't know about. There are people that get paid for writing down license plate numbers of vehicles that break a law. But there is no paper trail and the people don't realize that there are fines until they try to sell the vehicle.
Reality is though, that these people are writing up these "tickets" especially for business vehicles - whether there was an infraction or not... so that they can get paid. They are figuring that it is for a business... therefore the business has money. In fact, they have also offered to take a bribe (for a lesser amount) to not turn in the infraction. But remember, they are getting paid for every infraction that they write. (and there is no actual ticket nor proof needed - only their word). A friend of ours recently tried to sell a business vehicle and found that there were $5000 (or $40,000 pesos) of fines that he had no idea about.