It's difficult territory because at some level asking people to meet a certain standard to have a stall at a craft fair is, essentially, "gatekeeping".

But art sales are really the only gatekeeping there is in art, and it has to do with there being a literal gate to a limited space. (It's also usually not artists themselves doing the gatekeeping)

People who are engaged in art really ask so little of other people who want to engage with art — the barriers to entry are essentially non-existent except intent and willingness to learn and spend effort. Essentially every kind of expressive art is cheaper than a good computer; every kind of art has someone enthusiastically chipping away on the internet about it.

But when it comes to access to the physical space to sell physical work that is the result of effort and learning, someone does have to say: "this is not the right space for these kinds of things". The question is how do you judge and how do you say it without destroying enthusiasm.