FOR YEARS Avis in Chicago Ohare would try to scam me. If I was using the car for a lot of miles, I would buy the full tank, and sign for it as I went through security. EVERY TIME time I dropped the car off they would say it was "missed" and try to charge me for almost a whole tank at a MUCH HIGHER PRICE! Since many people are catching a quick flight, they just take the receipt given and turn in to the company on expenses. I would go in and get it corrected.
Gate attendent - "they NEVER change the contract even though I turn it in."
After numerous failures, I had a co. lawyer call Avis and no one from our company had an issue anymore.