Apparently, this story began when Harlan Ellison wondered to himself what the life of the shop keeper must be like in all of those fantasy stories that feature a mysterious magic shop that sells the protagonist some talisman or other that will, purportedly, bring them their deepest desires. He asks who would run such a shop, what can selling these trinkets to unsuspecting passersby can possibly benefit them, and where do they go when the shop inevitably disappears.
Ellison's explanation for these is very imaginative, and very science-fiction heavy for a very traditional fantasy trope. He creates a world in which these shop keepers are actually trading for time; secretly taking time and causing the proliferation of anti-entropic energy by selling what, to the future, are essentially toys, to key figures in history. This time and energy is in turn used by the people of this far future to remain animated in a universe that has entirely succumbed to entropy and dark matter. Heavy, I know.
But the important part of this story is really more about a particular shop keeper; an artist named Lhayne who is working tirelessly to buy the reanimation of his lover, Ahna, but whose own artistic impulse and moral compass runs counter to the necessities of survival. What's really at play here is not just an attempt to answer an idle question on Ellison's part, but an exploration of the problems of art and the artist in the face of necessities of life. Ultimately, Ellison seems to be asking which is more important to the artist: their art or their survival. And, more importantly, why one would win over the other.