Do you have evidence or references for the cheating claim? My experiences with proof systems (San Diego, Munich, Rennes, Antwerpen) is that there is moderately frequent checking and I've only seen one cheater (in Munich) once. Everyone else has had their proof when the inspectors came through. N.B. Don't cheat in Munich. It's an on the spot 50 or 100 Euro fine. The cheater was quite unhappy because he was a Frenchman who had merely misunderstood the instructions.

I do recall but can't find the reference to the cost analysis for San Diego that the cost of automated enforcement (gates, barriers, etc.) was much more than the loss due to cheating.

There is a strong cultural and local environmental component to cheating. I doubt proof systems would work somewhere like NYC or Paris now that the gate/barrier systems are so entrenched and with the let's see how we can beat the system attitude of many users.