Green’s Dictionary of Slang

1. (US Und.) a petty swindler.

1876		B. Harte Gabriel Conroy II 311: It is worthy of a short-card sharp and a keno flopper, which I have, I regret to say, long suspected you to be.
1914		Jackson & Hellyer Vocab. Criminal Sl. 35: flopper [...] in general use by money changers, switchers (substituters); flim-flammers.

2. (UK Und.) a criminal who pretends to have ‘slipped’ on a shop floor or ‘been knocked down’ by a slow-moving automobile; they then claim damages, usu. offering to take a quick cash payment rather than go to an insurance company; thus flop racket, performing such frauds.

1903		N.-Y. Trib. 10 May B1: By far the greater fraction of the beggars belong to the generic class of ‘floppers’ — that is, those who squat in the streets and ‘throw out’ their hats for coin.
1907		N.Y. Times 27 Jan. Sun. Mag. 4: [headline] Professional Mendicants, With Made-up Disfigurements, Return to Prey on City’s Charity. Fagin’s Nests Filled Again With ‘Yeggs,’ ‘Crust-Throwers’ and ‘Floppers’.
1928		Nottingham Eve. Post 12 July 1/3: 'Flopping' For a Living. Irving Fuhr [...] did 75 flops for Cohen, and then worked for the greatest organizer in fake accidents [...] Laulicht, who is now serving a sentence [for] 'ambulance chasing'. Laulicht described Fuhr as a 'first-class flopper', very quick to discover possible causes of [an] accident, and then [to] make false claims to recover damages for injury.
1949		Monteleone Criminal Sl. (rev. edn).
1950		Goldin et al. DAUL 72/2: Flopper. 1. In the accident insurance racket, one who is adept at hurling himself before automobiles, feigning serious injury, throwing limbs out of joint, etc.

3. (US Und.) a beggar who pretends to be crippled.

1903		N.Y. Tribune 10 May 17/1: The greater fraction of the beggars belong to the generic class of ‘floppers’ — that is, those who squat in the streets and ‘throw out’ their hats for coin.
1915		Morn. Tulsa Dly World (OK) 13 June 19/1: Flopper — A beggar who pretends to be crippled; squats on sidewalk near prominent corners; pleadingly holds out hand or hat. (See ‘Sap artist’).
1923		N. Anderson Hobo 100: [From A No. 1, The Famous Tramp] 3. Flopper. Squatted on sidewalk in business thoroughfares.
1937		‘Boxcar Bertha’ Sister of the Road (1975) 301: floppers. (Those who sit or flop down in front of a church or building and give the impression of being cripples.).
1949		Monteleone Criminal Sl. (rev. edn).

4. one who faints, collapses.

2009

J. Stahl Pain Killers 23: Guy’s probably a flopper. In this sun some boys just keel over and have seizures.