The Pemex in Tulum (across from the Chedraui) seems to be a "scam free" location. They actually go out of their way to point out the Zeroed pump and to confirm your payment. It seems as though that they are aware of the scams at other Pemex locations (in Tulum and other areas) and want to avoid getting a bad reputation. Just make sure that you get out of the car and apply common sense tactics and you will have no problem at this Pemex location. It is also the only Pemex location where the workers seem to understand/know English and want to have a quick conversation with you. This location also takes credit cards.