It's a shame that the article is so interesting in telling us about snake oil salesmen and the shenanigans and questionable claims involved in the trade, but it neglects to explain the direct origin of the phrase "snake oil salesman."

The phrase comes not from the ineffectiveness of snake oil, but rather from the common practice of selling counterfeit snake oil, that is to say selling some other liquid falsely labeled as snake. There was a famous Federal bust of a snake oil salesman, and after testing it was revealed that he was selling a liquid with beef fat instead of honest-to-God snake fat.