I am not sure why everyone complains all the time about this. It is very simple to place your receipt next to the display on the vehicle showing both the mileage and fuel level. I do this with a noticeable Hertz background to show it was taken at the facility during return.
I've never had to initiate showing Hertz this, as I've never been charged fuel, but nice insurance to have and takes 10-seconds of your time. And this simple picture shows fuel, where fueled, time fueled, mileage, and time returned.
Along those lines, I honestly don't even know why I fill the vehicles up, as my corporate rate has discounted gas based on fuel used, which is typically cheaper than the local gas station.
This brought up a thought. Could Hertz have changed their check-in procedure regarding topping off of vehicles during cleanup?. For those individuals that fill up 50-miles from the station, but car still shows full when returning. If when topping off vehicle during cleanup they put in more than 1-gallon, the charge gets placed? Just a thought.