Rental agencies should top off cars when they come in. This way there's no playing games with the needle is on F, but it's down two gallons because the last guy didn't fill it all the way.

I totally don't get the entire show a receipt thing. How hard is it to not fill it all the way up, get the needle to F and print a receipt?

One of the local HLE's will fill up every car that comes in. If it's over some amount (half gallon, gallon whatever it is I don't know) they will charge the customer. Considering there's at least four or five filling stations within two blocks of them, I don't have a problem with that at all.