Quacksalver

quack-salv-er* (kwækˈsælvər)

noun
1. a derogatory term for a person who dishonestly claims knowledge of or skill in medicine; a pedlar of false cures.
The medical impostors on the information superhighway are no more scrupulous than earlier quacksalvers who traveled along the streets of towns and villages. One notorious historical quacksalver managed to establish brand-name recognition that lasts to this day. Clark Stanley billed himself as the "Rattlesnake King," gathering crowds by killing rattlesnakes while delivering his pitch. For 50 cents a bottle, you could cure your toothaches, neuralgia, ankle sprains and pretty much everything else. Stanley claimed his snake-oil medicine came straight from an Indian medicine man and that his blend of snake oils worked miracles. When the Feds seized a shipment in 1917 and tested it, it was discovered that his snake oil was about 99 percent mineral oil and 1 percent beef fat, with traces of red pepper and turpentine thrown in the mix to give it a more medicinal smell. His business was shut down, but "snake oil" lives on in our lexicon to this day.**

Synonyms: charlatan, quack.

*This term actually comes from the Dutch: kwakzalver, meaning the same thing.
**My source for this example is a clever Discovery Health article.