...Or Your Money Back is a science fiction novella by Randal Garrett, first published in 1951, under the pen-name David Gordon.

There are lots of things that are considered perfectly acceptable ... provided they don't work. And of course everyone knows they really don't, which is why they're acceptable.... 

Randall Garrett (1927-1987) was an American science fiction and fantasy author. He was a prolific contributor to Astounding and other science fiction magazines of the 1950s and 1960s. He instructed Robert Silverberg in the techniques of selling large quantities of action-adventure science fiction, and collaborated with him on two novels about Earth bringing civilization to an alien planet.