Commenter GeeBax is right, the rails are narrow gauge, 3 feet to be exact, and worked by horse-drawn streetcars. The San Luis Potosi streetcar system wasn't electrified until the rather late date of 1914, according to this history site created by Latin America streetcar expert and old friend, Allen Morrison.
http://tramz.com/mx/sl/sl.html
As to the "sample room", I believe these were rooms at hotels where traveling salesmen displayed their wares to potential buyers. They've pretty much disappeared along with traveling salesmen.

The rail line seems to be narrow gauge, and it has no overhead catenary, so I presume it is not a trolley line, unless it was worked by horses? It also appears to end at the far end of the street.

You have to love the 8-legged cat!

You sure don’t want to fall off the sidewalk into the tree crevasse.