I once had a problem with an intransigent manager at Hertz in London who insisted that I hadnt filled up and who wanted to charge me for a gallon or so after I had just filled up a half mile down the street! I wondered how he knew.

He insisted on showing me that he could cram in more fuel and showed me his doing it, - when I knew I had just filled up! He pressed the hand lever on the pump and the fuel almost immediately started flowing all over the floor! ""There", he , "I told you it wasn't full!"

Hertz wouldnt believe that he was wrong on this: UNTIL I later produced the garage receipt, timed five minutes before the time of return!