“The Big Pat Boom,” Damon Knight, 1963 – Alien tourists on Earth create a boom in the sale of cow patties. Unexpectedly, they leave, causing a crash; new aliens arrive, creating a market for apple cores.
Comments: Read in Laughing Space.
Author: Wikipedia: “Damon Francis Knight (September 19, 1922 – April 15, 2002) was an American science fiction author, editor, critic and fan. His forte was short stories and he is widely acknowledged as having been a master of the genre.”