We agree. It is interesting that we have not purchased fuel in Mexico in many years without the attendant making a point of showing us that the pump was zeroed. Yes, it's possible probably to keep the pump going so that you can add to the total, but really??? Sounds like hard work.
Short changing? If we all paid cash for gas in our home countries, we'd probably run into it on a not irregular basis. Especially when full service is expected.
Our gas station experiences have been positive with a very very occasional glitch. Windshields washed, often all the rest of the windows, even in an RV, offers to check the fluids and tires.
Be sure to tip and be nice. We are visitors in Mexico.