The only reason to pre-pay is if you don’t want to be bothered with filling it up or if it is easier for you to make an expense report (i.e. one less receipt to deal with).
Yes, it is cheaper per gallon, but you buy the whole tank and no refund on unused gas. Also, and this is the most important and sneaky part, so excuse the all caps…
YOU PAY THE OUTRAGOUS AIRPORT TAX ON TOP OF IT!
So you might be shaving 50 cents per gallon, but that %20, 25%, 40%, whatever the tax % is is put on top of the cost of the tank, wiping away most savings.
Also, it doesn’t matter what the counter says, it is all based on what car you take. Which means if you got the free upgrade to an SUV, you are now paying for a SUVs worth of gas instead of a midsize car’s worth of gas.
As for the OP only getting charged $25 for ¼ tank, you probably got lucky. All the return agent does is enter 0 through 8 on the fuel left section on the hand held (0 meaning empty, 4 meaning ½, 8 meaning full), and then the car goes off, gets cleaned, refueled, and re-rented before anyone knows what happened. I usually gave customers who forgot to fill up or were running late a break.
-zoneguy