Various scams were reported as google reviews. Our experience: one of the employees approached us right after leaving Pompei train station and even had an official info booth INSIDE the station (looking like public tourist info). We told her no thanks, we already had a bus ticket to mount Vesuvius and showed her the key.
She lied to us and said, noo, VESUVIO is a town at the bottom of the mountain; only THEIR bus will take us to the crater; we have the wrong tickets. We should buy their tickets, and we have to decide now because the bus is arriving and there are only two tickets left.
So we purchased theirs. I reported the case at the police station in Pompei, but I am unsure if they will process it; no one correctly spoke English there…