"The vendor did not announce a price when buyers joined the queue, but people completing the transaction at the time the queue was joined were paying ‘X’ " isn’t legal in the UK?
That feels odd in a country where a couple of motor insurers have used random number generators when offering a price.
In my admittedly limited experience of Ticketmaster queues, I don’t recall Ticketmaster telling me prices until I got through the queue…and therefore I’d have no grounds to complain about bait-and-switch.
Within reason, the transaction is between Ticketmaster and me, and the price paid by someone ahead of me in the queue is irrelevant.
However it is possible that Ticketmaster did give me information when I was deciding to join the queue and I didn’t register the information. If that were the case, depending on what was said… that would definitely be a naughty bait-and-switch tactic.