Green’s Dictionary of Slang

(UK Und.) confidence tricksters, specializing in defrauding country vistors to London/New York.

a.1790		H.T. Potter New Dict. Cant (1795) n.p.: drop a set of cheats who make it their business to cheat and take in unwary countrymen at cards, &c.
1809		G. Andrewes Dict. Sl. and Cant.
1821		Flash Dict.
1835		G. Kent Modern Flash Dict.
1848		Flash Dict. in Sinks of London Laid Open.
c.1850		Duncombe New and Improved Flash Dict.
1859		Matsell Vocabulum 27: drops, or droppers Fellows that cheat country-men by dropping a pocket-book filled with bad money near their heels, and then pretend that they found it. By the aid of an accomplice, the countryman is induced to purchase it, with the avowed intention of finding the real owner, believing it to contain good money.