Fancy footwork similar to the gasolineras.
Pemex gasolinera on the lista negra advertise the lowest liter prices. Crooked pumps, lowest price. The newcomers, ARCO, BP, Chevron charge a few centavos high and at least for now offer litros completos. There is no comparison which is the better bet. Litros completos ends up a 20 to 1 savings over a few centavos discount.
BanNorte got two chances at my VISA both times BanNorte rendered ten percent fewer pesos than BanaMex.
In this area HSBC rejects all but Mexican cards.
Finding out who does what is simple, just ask a neighbor in an RV park.