From Wise Geek.com
Snake oill is both a legitimate product made from the oil of Chinese water snakes, and a derogatory term for a variety of products that claim to cure ailments but do not. The snake oil salesman, once a common feature in the US and in the UK, was a person who sold silver bullet cures for any illness. Originally, the initial snake oil came from China, where it is still used as a medicinal treatment to cure inflammation and arthritic conditions.
Real snake oil may actually have some health benefits, especially when it is made from the Chinese water snake. It’s commonly found in pharmacies throughout China and used as a topical treatment for joint pain. It does contain high levels of certain essential fatty acids that have been shown to reduce inflammation. Unfortunately, finding real snake oil can be a chore. You can find rattlesnake oil in the US but it tends to have only about a third of the fatty acids Chinese snake oil contains. Fish oil would be a better choice.
As traveling salesman peddled snake oil throughout Britain, where it was first patented in the 18th century, and the US, it was noted that most did not sell real snake oil. Many products that purportedly had oils from the Chinese water snake contained none, and were instead mixtures of camphor, some form of fat (often beef), and alcohol. The unsavory reputation of people selling snake oil began to gather steam as most people who bought the stuff found no benefit from using it.
Today, calling someone a snake oil salesman may be another way of saying that the person is particularly good at selling worthless items. There is something smarmy and untrustworthy about the snake oil salesman. This opinion is not shared in China where real snake oil can be easily purchased. Sometimes in the US, all homeopathic remedies are dismissed as “snake oil,” which is a generalization. Some non-traditional remedies are helpful and do have value, though taking them should always be done under a doctor’s care.
Traveling snake oil peddlers are often a feature of films set in the Old West. W. C. Fields played a fraudulent one in the 1936 film Poppy. Numerous others were just stock characters populating Western films. They are often portrayed as deliberately attempting to fool the public, though some people may have had great faith in the promised results of snake oil and other remedies.
As with any product, belief in the product’s efficacy can produce results that have nothing to do with the product. Attitude about how a product works can make some people feel better, evoking what is called the placebo effect. A good snake oil salesman might have such a quality sales pitch that a few people did find benefit from worthless products (not true snake oil). Therefore, the snake oil salesperson often escaped being thrown out of towns he visited. Alternately if he wasn’t so good, the salesman moved on quickly to the next town to avoid people demanding their money back, or insisting on violent retribution.