The gasoline station is a "whole nother thing". I've been frequenting Mexican fuel stations for many decades, and though some are pristine abd efficient, some others are proficient at fleecing the traveler.

Attendants get tipped at the encounter of the transaction. Five pesos is OK for someone who has been polite and dine his job - not quite a quarter dollar - ten is generous.

Always note how full your tank is and then note if the pump has been zeroed. Specify how much fuel you want as well as the kind if it's a multiple fuel pump - "lleno" (yeh-no)!is full, otherwise specify how many "litros" you want - then be sure that's what you get.

If they offer to check your oil, be there so they don't short dip the dipstick and show you that you apparently need a can of oil when you don't. It's not very likely, but make sure they don't pull a cable so you now "need maintenance". If you do need oil be sure they bring an unopened can and open it in front of you.

Be aware of how much money you're giving the attendant and say it ("quinientos pesos" - 500 MXP for example) and count your change.

Have someone watch the car to make sure nothing is pilfered.

Avoid the kids who might offer to "wash" your windshield with a can of water and newspaper - they probably don't work there, they may have silty water and reused paper, leaving your windshield scratched. Give them a couple of pesos (peso is about 18 to the dollar) and tell them "no, gracias". This gives them what they want and is useful for the occasional budding thug who might surreptitiously key or scratch your car if you're surly with them.