In Canada (and I’m sure elsewhere) there are surprise inspections where government inspectors show up at petrol stations and see if the pump actually gives you what it claims.
I volunteer for the pub equivalent of this.
I don't know if other companies do this anywhere but if you live in Ireland. Diageo have roles for people to travel around the country doing precisely this.
You're in luck. Measurement Canada has the authority to inspect pints. Typically they only act on complaints, though.
https://ised-isde.canada.ca/site/measurement-canada/en/buyin...
In the US every gas pump I've seen (I have not check the majority of states, but still a good sample) has a sticker on it stating inspections and who runs the state department that inspects them. Usually it is a yearly inspection (at least according to the sticker, maybe they do it more often I don't know)