Green’s Dictionary of Slang

1. (also flam-blam) nonsensical.

1664		C. Cotton Virgil Travestie (1765) Bk I 32: And fobb’d Queen Dido off / [...] / By telling her a Flim Flam Prattle.
1683		Fifteen Real Comforts of Matrimony 57: Why then did the woman […] endeavour to blind him with her flim-flam-stories.
1875		Junction City (KS) 5 Aug. 1/8: ‘Oh yes, gimme ten cents worth of hair-pins [...] The gal is always wanting some flim-flam thing’ .
1888		Huddersfield Chron. 14 Aug. 4/3: It is not really a system of elementary education at all, but a system largely taken up with flim-flam instruction.
1890		Manchester Courier 26 Apr. 14/6: It’s wonderful what flim-flam noshins they do get up to nowadays.
1898		H. Macfall Wooings of Jezebel Pettyfer 171: All t’udder talk are flam-blam foolishness.
1904		E.W. Townsend ‘Chimmie Fadden’ 25 Dec. [synd. col.] ‘It’s philos’phy,’ he says. ‘What kind of a flim-flam game is dat?’ I says.

2. tricky, cheating.

1902		C.L. Cullen More Ex-Tank Tales 100: Don’t youse try none o’ dat flim-flam woik wit’ me.
1920		Sun. Post (Dundee) 4 Apr. 3/5: The nation got tired of that sort flim-flam game.
1940		E. Curry Hysterical Hist. of Aus. 40: A pretty dod gasted ding-whanged, flim-flammin set of thieves, rogues and vagabones.
1956		H. Gold Man Who Was Not With It (1965) 303: Past the tall flimflam captains’ houses with the wooden roosts at the top.