I was in DEN last week and returned my car at the counter, as the Express people were gone for the evening. Told the agent I refueled the car. In fact, I told her that I had just paid the highest price I've ever paid for regular unleaded gas to date-$4.15/gal at the station down the street from Hertz. She told me that gas at that station was $3.89 earlier in the week. I got my rental receipt and caught the shuttle back to the airport.
It was not until I arrived home that I discovered that I was promptly charged for $31.22 for gas, at a whopping 7.99/gal!!
I called Hertz, spoke to billing and told them what happened and that I had a receipt to prove I refilled. In fact, I refilled not 3 minutes before returning the car!
Needless to say, I got it corrected and credited back to my credit card.

However, I can't help wondering if this was this an honest mistake or a malicious act by the agent at counter, trying to sneak a charge on my bill? Even moreso since we had short conversation about my refilling the car and how much gas was at the station down the street?

Hmmmm....
I've been renting from Hertz for years and this is the first time this has ever happened. I usually check my receipt, but this time I was in a hurry to catch my flight-and didn't.
Take home message is-check your receipts, people!