The story involves a shop owner and a time-travel mirror. The shop owner tells stories of customers going through the mirror.
The shop owner playfully demonstrates the power of the mirror to customers by putting his hand inside and doing things like poking himself. Then, he tells the story of someone who goes through the mirror and had a wonderful experience.
After that, the shop owner says that that very story, told to another customer, was enough to convince this other customer to go through the mirror. However, this second customer's experience ended up much worse. I think it involved problems with his partner, and I remember a scene in which one of the customers arrives at the block in which his partner lived, only to find they no longer lived there.
It was set in an Arab-like world, before electronics. It also involved traveling between cities.
I read this story between 2015-2020. It was part of a short story book. The author is American.