Art dealer Sonia Dutton was at her gallery on the Lower East Side last fall, where “Night Drawing,” Boston artist Rose deSmith Greenman’s debut New York exhibition, was on view. The untrained artist began drawing only in her seventies, but her still lifes, often made after dark with humble materials like everyday markers and ballpoint pen, bristle with energy. In came a museum curator who expressed enthusiasm about the show, and even interest in acquiring a piece. But that news came with a pitch many dealers have come to expect, and not necessarily relish. It goes a little something like this, Dutton said: “We love the show. We love the work. We’d love to have something for the museum’s collection. But I’m not sure we have the funds for it.” In practice, that can translate to, “Who can you find to buy it for us?” This presents a mixed prospect for the dealer: the chance to have an artwork enter a museum collection is a coup, but it is tempered by the...