I think we can all agree no symphy.
I have had a number of cars I have driven a short while and its dropped which tells me the last renter has not filled it properly. I do get the odd few that the branch has filled and i get a decent service from it. Yesterday I drove 80 miles and it still shows full but I parked on a slant and I notcied the needle dropped slightly.
I guess the moral is fill it up! Its unfair on the next rental. I always work out how many litres I need to put back in to get back to full, usually means I get the click a few times but I know I have filled it back up properly and its fair on the next person