Beware phantom after car return charges from Avis Budget. 2nd time it's happened to me

Beware beware beware those mysterious charges that appear on your card after you drop the vehicle off. Second time this has happened to me. I book via a UK aggregator because it's massively cheaper than booking locally - an issue in its own right, why ******* locals? When I dropped off the car, fully refueled, I asked the drop off person if there would be any charges over and above the tolls incurred. NO was the answer. I asked for a sign off but he couldn't give it to me. E voila, 2 days later I get a charge for....you guessed it. Refueling! This is ********** surely?