I have had two guns that were not the gauges stated when sold on GunBroker.
In both cases GunBroker was zero help. One was a 12 which turned out to be a very light 10 and the other was a 16 which again turned out to be a light 12. How hard is it to drop a shell into a gun I wonder?

The other mistakes are often hidden flaws that creative camera angle have omitted in spite of many pictures. Worse have been a couple slightly out of focus photos which clearly were meant to hide problems. Or clearly mistaken facts in the descriptions.