Price of gas in Mexico

Our experience over the years has been that "cajero automaticos" (ATM) always give the best rate. We see the rate posted in the bank window and then go to the cajero at that bank and find we get a better rate. The rate at retail shops etc. have been at 12.5 for many years. We would never change at "cambios" in either Mexico or the US. I have no idea how the cajeros are set or adjusted but it seems they may be computer connected to the main money rate market. That said - we also never go to stand alone cajeros - only a cajero located at an actual bank give the best rate. Kiosk stand alone cajeros are privately owned with the intention of making money - you will not get the best rate there - and they may even take your card and give you nothing in return. Go to a bank.