The Role of Auction Houses in the Private Art Market

When auction houses and galleries sell works of art are they discriminating between buyers on these kinds of terms. Do they ask whether the art is likely to be shown at all or made available for future exhibitions like this? Well I think we need to distinguish here carefully between the Sotheby's and the Christie's of this world and the big gallery is like the gozier or pace or something like that. In the in the gallery space right where the middle the broker is acting not between a buyer and a seller but between an artist and the market.