Several of the gas station shops that I do specifically want to test the operation of the credit card processing machine at the pump (and whether it produces a receipt). If that was the case with yours today, then I fear that you omitted large portions of the shop since gas was available. If gas is not available (I had one of those a few weeks ago when a construction crew cut the electric line), that is another story and I have been paid after explaining the issue and taking photographs. Unless the shop is one where you have to time to the second how long it takes to dispense 2 gallons of gas, I have been told that there is actually not a minimum amount that I have to purchase (Green and White; Red, White, and Blue; and Yellow brands). I worked for a division of one of the very large oil companies and I assure you that using a lower octane gas will not harm your car. It MIGHT run a little rough and have worse mileage, but you could always dilute it at the next stop with 93 octane or just more 91 octane. Your engine would be fine.
Shopping Southeast Pennsylvania, Delaware above the canal, and South Jersey since 2008