Recall the old-style house type outlets in the U.S. Just two vertical prongs, no ground. That is what most of the older outlets in Mexico are wired with.
So, reverse polarity is really easy to get.
When we travel in Mexico, I have a 15 amp male to 30 amp female adapter with a cut off ground prong that I can turn over to get correct polarity. And, a 6' ground wire carefully wired to the ground lug of the adapter with last 9" bare copper. Wrap it around a metal pipe or attach to rod driven into ground.
Never a problem in 50,000 plus miles south of the border. Ya, still have to monitor voltage. Have seen both too high and too low-- sometimes in the same CG at different parts of the day.