Green’s Dictionary of Slang

(UK Und.) a confidence trickster.

a.1790		H.T. Potter New Dict. Cant (1795) n.p.: swindling-gloak a cheating dirty fellow – an imposter – a cheat.
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.