"Quack" as a derogatory term for a scammer healer has a long history. The word derives from "quacksalver," a term coined in the 1570s from the Dutch "kwaksalver," literally "hawker of salve," according to Online Etymology Dictionary. The term has versions in German (Quacksalber), Danish (kvaksalver), and Swedish (kvacksalvare).
|The Quacksalver by Rembrandt, 1635|
As Europe became increasingly urbanised throughout the 16th century, and people moved away from small communities, it was less and less possible to rely on a local and well known wise woman or healer (often your own mom). Apothecaries or physicians - the university trained variety of doctor - were expensive, and might not have the miracle cure you were looking for.
Enter the snake oil salesmen.
A huge part of the quacksalver's game was performance, including an enactment of the miraculous curative properties of whatever cordial, syrup, or salve that was for sale that day (usually performed by an assistant who was an employee of the quacksalver). Travelling quacksalvers used a form of theatrical performance familiar to us via the late night infomercial. (There is a fabulous example of this in Andrew Miller's wonderful novel Ingenious Pain.)
Their actual healing skills might be dodgy, but they would sell you a cure at an extremely reasonable price. As time went on, the term "quacksalver" came to apply to any would be healer with questionable skills, including the barber-surgeon. ("Physician" did not equate to "surgeon" originally - if you needed surgery - a tooth pulled, a boil lanced, or something cut out or sewn up - you went to a barber, not a doctor).
|A typical day at the barber-surgeon's.|
|By object... Via Medico Della Peste|