The only place I've seen them in action in person was at a "random" truck inspection. Local police pulled over "random" commercial trucks in a certain area near a major road near a major highway and direct them to drive to a certain parking lot nearby.
Anyways, before the waiting MTO officer came to look at any paperwork or anything, two (yes, two) finance officers came and checked the fuel tank. Looking for any dyed fuel (farm, less taxed) or residue in the tank. 15 seconds for the two of them to look and their inspection was completed. Then they stood around and waited for another truck to pull in.
Other than that, I don't know.