Green’s Dictionary of Slang

1. (US) a swindler.

1891		Telegram Herald (Grand Rapids, MI) 25 Jan. 10/2: ‘I defended the “handshaker” of the gang which swindled a syndicate of three men. [...] The “handshaker,” you know, is the mn who meets the victim when he arrives in the city.
1896		‘Frederick Benton Williams’ (H.E. Hamblen) On Many Seas 406: I know ye well enough. [...] Clear out, now, before I call a policeman and have ye locked up! [...] You are one of these handshakers; that's who you be!
1905		F. Hutchison Philosophy of Johnny the Gent 5: What's the matter with the Handshaker an' the Wise Crackin' Kid? [...] Ain't they speakin'? Them guys gimme a pain in me foot.

2. (US) an insincere person.

1893		St Louis Post-Dispatch (MO) 3 Dec. 17/7: ‘The genial’ [is] a professional appreciator, a man who laughs at everything, pays for nothing and is universally sympathetic. ‘he hand-shaker’ [is] synonymous.
1900		Ade More Fables in Sl. 178: When he had to go out and Rustle for a Job he was a Busy Hand-Shaker once more.
1925		S. Lewis Arrowsmith 87: I was afraid the old kid was going to get tied up to – to parties that would turn him into a hand-shaker.
1936		Mencken Amer. Lang. (4th edn) 573: The greater part of the American vocabulary came from the Regular Army, and some of it was of very respectable antiquity, e.g., hand-shaker, Holy Joe (for chaplain) [...] and punk (bread).

3. a toady, a sycophant.

1898		S. Crane War Disptaches 193: The American soldier alludes often to the natives here as handshakers. It is his way of expressing a cynical suspicion regarding all the Viva Americanos’ business that he hears and sees in this city.
1918		Oklahoma City Times (OK) 21 Aug. 7/2: A recruit who tries to buy his way or hangs around an officer [...] waiting to do his bidding, toadying to him, is known as a ‘handshaker’. In the army a ‘handshaker’ ranks lower tha a worm.
1927		(con. 1914–18) L. Nason Three Lights from a Match 140: These handshakers will let the Boche through on us.
1933		Ersine Und. and Prison Sl.
1943		J. Mitchell McSorley’s Wonderful Saloon (2001) 6: Although by no means a handshaker, Old John knew many prominent men.
1953		T. Runyon In For Life 169: I couldn’t give officials deserved credit without getting my back chewed on for being a handshaker.