Just had this happen at CLE with Thrifty/Hertz. I returned the car full, agent admitted it was full but still charged for gas which I saw at the airport when they sent a pdf of the bill. I called, they 'graciously' agreed to refund me although still saying it only had 7/8th tank. When the office called me after I filled out their survey, they admitted I returned the car with a full tank. Got a half-hearted apology of 'these things happen.'