Green’s Dictionary of Slang

(US) a swindler.

1898		Mt Sterling Advocate 29 Mar. 5/2: There are so many tricks practised in horse dealing. A certain class of men known [...] as ‘gyppers’, carry on a trade which brings into use ‘tricks’.
1919		Wash. Times (DC) 29 Jan. 17/1: The judger Meets and Optimistic Gypper [...] I gotta hand it to you — that was the slickest job that’s been pulled off around here in years.
1919		A. Baer Two & Three 20 Dec. [synd. col.] Flat sharks and food gypers and coal cheaters.
1921		N.Y. Tribune 6 Mar. 6/5: It is ordinary common sense to avoid the gypper and the used-car dealer.
1924		Nott. Eve. Post 1 Nov. n.p.: A party of American ‘flat-catchers’ [...] have just landed in England. These birds of prey are known in Amerca as ‘gyppers’.
1929		H.C. Witwer Yes Man’s Land 245: ‘Now I’ll tell you one!’ snarls the taxi driver. ‘You cheap gyppers is gettin’ on my nerves!’.
1963		L.F. Freed Crime in S. Afr. 107: A ‘gipper’, a ‘fiddler’, a ‘diddler’, a ‘kitsler’, or a ‘kinsler’, a ‘chiseller’, or an ’amuser’ is a swindler.
1970		in P.R. Runkel Law Unto Themselves 258: Oh, that dirty, bloody gypper!