[caladri]

Your problem is actually with the organizers. You don't care a bit about random venues except for where organizers of events you are likely to attend decide to use them, I would guess. Therefore, if you have a problem with the venue, you should take it to the organizers, and take it up with them at the time, e.g. by leaving with your student, because wrangling the venue is what they're doing as organizers setting up an event.

Other venues are much more reasonable about this sort of thing. I have a friend who is banned from all Microsoft buildings, including non-Microsoft events hosted by Microsoft. He was informed clearly in writing, and knew the reason for his being banned. That makes Microsoft-operated venues more appealing (on at least this axis) than Yelp ones, since organizers of an event can't be sure that attendees will actually be able to enter. In the Microsoft case, at least a person seemingly knows whether they can attend.