Case in point: the proliferation of furcons.
Which has been good & bad with some of the shadier smaller conventions, mismanagement and overgrowth of some of the larger conventions into worse hotel/con experiences.
But to go beyond furcons, nerd conventions in general are now dealing with gen-ai art showing up in lazy con hosts who are just trying to scrape money from the hobby. Struggling to police makers who just download common models online and try to sell budget 3d printed crap at dealer dens / artist allies, taking spaces from actual artists.
In a healthy community people will notice crap and simply won't buy it, which discourages merchants from selling crap. If that's not the case, then it's quite likely that the community has bigger issues because they cannot distinguish crap from good items.
I mean, if someone shows up with hand-made crap then the community should also push it out, whether it's hand-made or mass-produced is pretty much besides the point.
Regarding the cons themselves, of course there are good ones and bad ones. That's how it is with everything.