Is Artio Gallery a vanity gallery?

Recently I was selected to participate in an international art show but am being asked to pay an exorbitant participation fee as well as a 70(artist)/30(gallery) split.

Is there ever a reason, other than an art fair where an artist has their own booth, to charge a participation fee AND split the sale?

I don’t want to miss an opportunity but I also don’t want to waste my time and money on a vanity gallery.