There have been a few times that either I have been running so late that I don't have time to wait for the receipt to print or there is no attendant (often with Hertz). I always take a picture of the dash showing a full tank of fuel and pictures of the exterior. This has been very helpful when Enterprise has decided to charge me for a partial tank of fuel on multiple occasions. (I also always take lots of photos of the car when I pick it up - never know what the rental car company will try to pull). The time stamp of when the photo was taken would be helpful here.