I use national every week and have had a couple scenarios play out.

I never prepay because of the price, if I forget or am running behind and did not get the car filled up they are usually pretty good about being FAIR. Often times they would ask if you filled the car up and I would say "dang I forgot, but I have time to go do it" and they will barter with me to only charge say 2/3 of what is actually missing from a full tank.

Last time in San Antonio the guy was very cool and charged me a 1/4 tank when it was just under 1/2 tank.


They also now allow you to prepay for a 1/2 tank which is not terrible.