Everyone loves a good story. Language itself has evolved for story-telling, as have our brains. Backstories help sell everything from You Tube personalities to paintings. Works that are intensely personal, unless opaque/hermetic, the commonality of human experience assures some connectivity.
In a way, lacunae in a backstory are often filled-in by the viewer in this regard, and it is a complex thing, because cultural factors, formal aspects, context and more enter into it.
How does the savvy gallerist use backstory to increase sales? He can infuse it into each work, which is time-consuming and labor intensive or better yet, have the artist present to do the same, preferably by talking about his work.
Some gallerists take the path of least resistance with this issue by relying on shared backstories. Stories that are already embedded in the viewer. A good example would be Pop Art. To give one example of a gallerist that is working this formula well, Chad Mize of Blue Lucy does this consistently with very good, albeit uneven, results.
A great example is the current show at their Ybor City location, "Toons". Artists came up with paintings themed around cartoons, done in the usual Blue Lucy same-size wooden boxes. Easily identifiable with the original characters, these works had a collective backstory built into the viewers. Many of them were offering sentimental memories of the characters depicted to their friends as if talking about a common acquaintance or relative. No need to inject backstory, it is already in the memory of most prospective buyers.