I had that happen once. But I always ask for the exact amount like $2,000. pesos and I come out of RV with that amount. He pulled that with the help of an accomplice. He got my attention just as I handed the attendant the $2,000.00 the other guy got me to turn my head and then the attendant said senior your $450.00 pesos short.
I laughed at him, and speaking Spanish I told him I had counted the money previously. He insisted, I made him empty his pockets and there was a crumpled $500.00 peso, he got my wrath and our fellow RVers who spoke Spanish read him the riot act!
Senor mi culpa perdoname por favor.
Best case count your pesos out to the attendant this will stop this scam, but I have caught them at other scams.
Se intelegente amigos.