I got a $80 bill from Hertz for returning a compact car without gas. I had returned the car with a full tank of gas though!

There is no way to resolve this on the phone, so I filled out their online form to dispute the charge.

After not hearing from Hertz for 2 days, I disputed the charge with my credit card. The credit card instantly refunded the entire cost of the rental.

Within 12 hours of the refund, I got an email from Hertz saying they were sorry about the accidental charge and that they'd give me a free one day rental.

Ultimately they sent me a bill for the cost of the rental minus the gas and threatened to take me to collections if I didn't pay it.

I never got my free rental.