I guess that’s up to the individual company and their policies. At our company, if you bring us a 20 pound bottle we charge you for 20 pounds no matter how much goes into it because there’s more to it than just pumping propane into the tank. We do a visual inspection and check the certification dates on every tank because that is required by law. We have to determine the tank’s tare weight (TW) and water capacity (WC) then refer to a special chart that tells us what the water capacity is in pounds, then do the math conversion to figure out how much we can pump into that specific tank to reach the final gross weight after we have taken a beginning weight before the fill. We inspect the valve, replace any damaged or missing dust caps, and replace any damaged or illegible warning labels which are also required to be on there by law. If you bring us a bottle that has a plastic shrink wrap label like AmeriGas and blue rhino, we cut those off and replace them with adhesive stickers because those plastic wrap labels collect condensation underneath and rust the tank which is a disqualification for the visual requalification. If we find a tank that is out of qualification and a visual inspection indicates that it is OK to refill, we have to do another step and apply our inspection label and record that, including the tank’s serial number, tank size and technician’s initials in our records to indicate that that has been done. So, if a legitimate company is doing everything correctly and not taking shortcuts, I don’t see any reason why anybody could complain about paying for a full fill if you know you are receiving something safe in the end that has passed all the legal requirements. That doesn’t even to begin to touch the hours of certification training and millions of dollars in liability insurance we are required to accumulate and to carry. I don’t consider us to be unscrupulous.
Edit: punctuation and spelling