Soooo......What the heck is a vanity gallery?
These galleries offer their gallery space for a fee which must be paid up front. Unlike other galleries this fee often pays the bills for the business so they don't need to worry as much as regular commercial galleries about selling the art. This means that there is less concern about the style and quality of the work.
In truth the term vanity gallery is a bit derogatory. This is because these galleries have the potential to use the artist's ego to make money. Ie. an unseasoned new artist might really want to have the experience of having a show so that they can feel good about their art and themselves.
I'm not saying that all of these spaces are negative .... or positive for that matter. The one's that I have come across did not temp me in any way but I feel like there should be more galleries that operate in ways that are divergent to the norm. Someone is going to create something between a gallery and pop-up shop that really works - I have faith in that. Perhaps it's already out there!
There are other issues that hide in the idea of a vanity gallery. For me I would be concerned that the sales reps may not be very motivated to sell the the work since they have their bills covered and the gallery may not be excited about selling the work since they aren't being choosey enough about bringing art into the space that they are really passionate about.