comes from the 19th-century American practice of selling cure-all elixirs in traveling medicine shows. Snake oil salesmen would falsely claim that the potions would cure any ailments. now-a-days it refers to fake products.
"why did you buy that snake oil? it does absolutely nothing!"
any dubious or fraudulent remedy or cure (The route of the fraud the word is derived from resulted from a misunderstanding of a traditional Chinese joint and muscle painkiller derived from the skin of the Chinese water snake)
That snake oil is so obvious. When will people learn?