shark-gull

shark (“to swindle; to trick”) +‎ gull (“dupe; mark; sucker”)

shark-gull (plural shark-gulls)

1. (obsolete) A confidence trickster; a person who preys on simpletons.
   • 1604, Thomas Middleton, The Black Book; republished in The Works of Thomas Middleton‎, volume 5, London: Edward Lumley, 1840, page 524:

     Complainest thou of bad doings, when there are harlots of all trades, and knaves of all languages? Knowest thou not that sin may be committed either in French, Dutch, Italian, or Spanish, and all after the English fashion? But thou excusest the negligence of thy practice by the last summer's pestilence: alas, poor shark-gull, that put-off is idle! for sergeant Carbuncle, one of the plague's chief officers, dares not venture within three yards of an harlot, because monsieur Drybone, the Frenchman, is a leiger before him.

• conman, sharker; See also Thesaurus:confidence trickster