I always ask for a set amount - for example 2000 pesos. I can't see how they can cheat on that as long as you check that the gauge is on zero before they start.
I find that to be false at my station...
I fill up a 5 gal tank and a 1 gallon jug of gas for our lawn equipment.
That's the easy way to verify the accuracy....
an empty 1.5L wine bottle will work...
Test it.... and then dump in your tank
Next you'll be telling us the wine makers cheat on their bottles !!!! hehehe
i'm told that calibrating those newer pumps is not that easy. in other words it's not something any given dimwit can easily pull off. kinda like other electronic scams, you have to have know-how to do it.
In the US( Massachusetts) their is a dept. of weights and measures that check the pumps regularly ,doubt jf they do that here.
We have one of those here in Bavaro, down by the Palladium. I am averaging about 25mpg and my tank was showing 105 miles left to empty or roughly 4 gallons. I asked to have the guy fill the tank. My 15.3 gallon tank amazingly held 18.7 gallons!!!! He argued with me and it was obvious at that point I was not going to win the battle....UNTIL....I opened the owners manual and showed him, that even bone dry, the tank holds 15.3 gallons. I even went to Kia's official website to show him. He refunded me the difference to 15.3 reluctantly as I could not prove there was 4 gallons in the tank prior to the filling. I no longer go to that "AMABLE" station...needless to say.
Every tank will have some "reserve room" I work at a new car dealer and we often pump more than what the owners manual says from brand new.