Green’s Dictionary of Slang

1. anything that will serve to dupe the public.

1821		W.T. Moncrieff Tom and Jerry I vi: Do you think we shall get the flat-catcher off to-day? [...] here’s three swells coming this way – that one in the middle, looks like a flat, we must try it on him.
1835		G. Kent Modern Flash Dict.
1838		R.S. Surtees Jorrocks Jaunts (1874) 234: She’s always on the road, and lives now by the flats she catches between Paris and the coast.
1848		Flash Dict. in Sinks of London Laid Open.
1852		Kendal Mercury 14 Feb. 3/3: A ‘flat-catcher’ (story to gull the public, like the one we have just narrated, would scarely be credited.
1865		R.S. Surtees Facey Romford’s Hounds 119: The horses [...] were almost all good flat-catchers, well calculated to please the eye [and] christened with high-sounding names diametrically opposite to their respective qualities.
1882		Eve.News (Sydney) 24 Feb. 4/1: [of a racehorse] Rather a flat-catcher, Tom [...] Too much action for a hunter, and too little body. H [...] Though he’s not a bad goer.
1890		C. Hindley Vocab. and Gloss. in True Hist. of Tom and Jerry 174: FlatCatcher. A man, woman, or any article intended to take in the public.
1890		Sporting Times 11 Jan. 3: Our friend makes such an offer for the horse that the cavalry colonel is forgotten, and Mr. Snaffle parts with one of the most worthless ‘flat-catchers’ he has ever had the fortune to own.
1894		Truth (Sydney) 11 Nov. 6/4: A horse by Cobweb, called Flycatcher, is rather well named, but I think he is somewhat of a flatcatcher.

2. (also catcher, country flatcatcher) a confidence trickster, one who indulges in ‘sharp practice’.

1828		G. Smeeton Doings in London 68: ‘The Fancy,’ who are technically called flat-catchers, and who pick up a very pretty living by a quick hand, a rattling tongue.
1832		Satirist (London) 8 July 223/2: George Hassell offers himself as flat-catcher to the club [...] having had experience in plucking and macing, he might be useful if be could be kept sober.
1840		N.Y. Herald 15 Jan. 2/4–5: Flat catching. [headline] [...] before him stood the identical flat catchers, who it seems had tried the same game on Mr. W., with whom it was ‘no go’ [Ibid.] 2/5: It seems almost a miracle that the catchers did not escape, as they were not detected until they were getting off the last ‘drop of Cogniac’ in their possession.
1848		Sth Aus. Register 16 Dec. 2/1: [I]n giving you good advice, I expose myself to the land-sharks here whose open jaws will soon swallow you up, unless you keep a sharp look out [...] We are nearly all flat-catchers here.
1856		H. Mayhew Great World of London I 46: ‘Flatcatchers,’ or ‘ring-droppers,’ who cheat by pretending to find valuables in the street.
1859		Bell’s Life in Sydney 16 July 3/2: I don’t know if you’re a fisherman, but you were there on Monday catching flats (loud laughter).
1861		Old Roman Well I 113: He has been a ‘shoful man,’ and a ‘smasher,’ and a race-course flat-catcher.
1870		Northern Echo 3 June 3/3: Our own ‘right little, tight little island’ en has a few of the swindlers we spoke of in a former article [...] We do not [...] allude to the ‘country flat catchers,’ as for upon the whole, they must be considered rather a meritorious race of gentlemen.
1870		Eve. Jrnl (Adelaide) 10 Dec. 3/2: [H]e believed the persons alluded to were simply here on a flat-catching expedition, and if they could get people to take shares, depend upon it tbey would do so.
1877		S. James Vagabond Papers (3rd series) 136: You have to go into general business. You must be a magsman, a pincher, a picker-up, a flatcatcher, a bester.
1882		Sydney Sl. Dict. (2 edn) 4: Flatcatchers - Those who ‘work’ by false pretences and by fraud.
1888		Shields Dly Gaz. 28 Nov. 3/1: A ‘flat-catcher’ is a cheap Jack at a fair. He offers a purse for sale, pretends to throw three half-crowns into it, and disposes of the lot for eighteenpence.
1894		Truth (Sydney) 4 Mar. 4/7: Banker Bullion lodged for a year or two with Fleecem of the ‘Flatcatcher’s Arms’.
1949		Monteleone Criminal Sl. (rev. edn).

3. in specific use of sense 2, a thimble-rigger n. (1)

1827

J. Wight More Mornings in Bow St. 41: Minor members of ‘The Fancy,’ who are technically called flat-catchers, and who pick up a very pretty living by means of a quick hand, a rattling tongue, a deal board, three thimbles, and a pepper-corn.