The out and in mileage on the rental agreement and receipt are one thing; the actual odometer readings are another. If you do not look at the odometer when you pick up and return the car, and compare those readings to what appears on the paperwork, you are subject to the kind of aggravation you are now experiencing.

Whenever I return a rental car, I snap a picture showing -- in one frame -- both the fuel level and the odometer reading. It's unfortunate that we have to do this, but it's really your best protection.

And if there's is a significant discrepancy between the "out" mileage on the rental agreement and the actual odometer reading, I do not drive the car off the lot until getting the rental agreement corrected.