Measuring by volume dispensed like gas pumps would be less likely to be abused. I can just lift the cup slightly as its filled and pay less.

Years ago at Universal for Halloween Horror Nights they used bottom fill beer dispensers. They had a connector on the bottom of the cup so you could grab a cup pop it down on the machine and keep going. Say 15 beers in seconds. The beer fills to the exact height needed with the exact desired foam amount on top. No over poors or needing to have any loss. Time was cut down drastically. The cups had to be expensive, but when your charging $10 for $1 with of product you don't have to worry to much about cup cost I guess. I remember thinking at that moment American Capitalism has peaked haha.

This but in Oregon you'd get yelled at for doing it yourself. :p

Edit: Huh, turns out they lifted that ban in 2023 so now people can pump their own gas.