Green’s Dictionary of Slang

shark v.

also shark on

1. to cheat, to defraud, to steal; thus sharking n. [shark n. (3a)].

Bk of Sir Thomas Moore facs.(D) (1911) I vi: Other ruffians as their fancies wrought [...] woold shark on you.
[UK]Beaumont & Fletcher Honest Man’s Fortune III iii: You know you can shark, though you be out of action.
[UK]Middleton & Rowley Spanish Gypsy II i: Some of them do but shark, and so do we.
[UK]J. Earle Microcosmographie No. 75: An ordinary honest Fellow [...] do’s it faire and above boord without legerdemaine, and neither sharkes for a cup or a reckoning.
[UK]Horn & Robotham (trans.) Gate of Languages Unlocked Ch. 83 817: A sharker (shifter) or make-shift sharks for money.
[UK]R. L’Estrange Fables of Anianus (1692) CCXLI 218: It was Nature that taught this Boy to Shark.
[UK](con. 1840s–50s) H. Mayhew London Labour and London Poor I 384/2: Us sailor chaps sometimes sharks the Custom-house lubbers, sharp as they are.
[Aus]Sun. Times (Perth) 24 Nov. 4/8: In his sales of hogs and hay / Oft the cocky’s sharked.
[UK]‘Guns, Q.F.C. & P. Theeluker’ Middle Watch Musings (4th edn) in DSUE (8th edn) 1984.
[UK](con. WWI) Fraser & Gibbons Soldier and Sailor Words 254: Shark, To: To steal.
[UK](con. WWI) F. Richards Old Soldiers Never Die (1964) 67: The head of that firm should have been [...] shot for the way they sharked us troops.
[US]P. Crump Burn, Killer, Burn! 115: I been sharked out of fifteen bucks!
[US](con. 1945) E. Thompson Tattoo (1977) 293: He [...] combed his hair into a gelatinous country pomp and tithed his pay and tithed the vigorish on his sharking.

2. to treat unfairly, to victimize [SE shark].

[US]H. Ellison ‘May We Also Speak’ in Gentleman Junkie (1961) 30: There was the simple way out of sharking someone else. Making someone else guilty.