Auction, either Sotheby’s or Christie’s (https://www.artsy.net/article/artsy-editorial-why-sotheby-s-and-christie-s-don-t-operate-like-other-duopolies https://w

Auction, either Sotheby’s or Christie’s (https://www.artsy.net/article/artsy-editorial-why-sotheby-s-and-christie-s-don-t-operate-like-other-duopolies https://www.artsy.net/article/artsy-editorial-why-sotheby-s-...).