What companies commonly do if you pay at the pump is your credit card gets authorized/temporarily charged for $100. Then you pump in $75. Then later it gets worked out that you get $25 back. And by later it's usually the next day or two after. None of it is instant unless you pay inside in which case it's like paying for anything. A lot of the gas stations up north here are used to trucks filling up way more than $100 and then take out $150.