Same happened to me with Budget, did know i had to show the receipt if under 75 miles They were the only rental open on a late arrival no taxis and long Uber wait time. I had an attended check in, no questions asked but when I got the receipt it had the fuel surcharge. Attendant just said "you didn't show me your receipt you have to go to the counter now"
Of course after waiting in long line, showing the receipt and getting the adjustment I was informed the policy is clearly on the signs (Points to a little tiny sign on the wall) and on my contract that I'm required to produce a receipt when returning
Ok yes my bad etc. but a simple inquiry for the receipt might be better customer service when they record the mileage with me standing there. Lesson learned and I show the receipt any time I use Budget which hasn't been much since then.