Actually have seen the above a few times too many ! Putting 29 gal. in my 26 gal tank where I was just above the empty mark when I pulled in to get gas in the first place.
Another time I had a 5 gal gas can to fill up , I called everybody over at the station that was fueling up their vehicles to show them that I fit 7 gallons of gas into a 5 gallon can ! The station clerk and I had words , I left paying for 5 gallons.
Next morning I called the local Weights and Measures , they went to that station, checked every single pump, 3 of the 6 pumps were off in favor of the station...
So yes it can and does happen...