Green’s Dictionary of Slang

to cheat, to defraud, to victimize.

1832		Satirist (London) 10 June 191/2: the sporting gentlemen have suffered themselves to be most completely done at York [...] Even Bland, the former co-partner with Richardson, has been let in to the tune of 2,000l.!
1855		Thackeray Newcomes II 307: Affairs had been going ill with that gentleman – he had been let in terribly, he informed me, by Lord Levant’s insolvency.
1859, 1860		Hotten Dict. of Modern Sl. etc.
1861		Hills & Plains I 43: All ‘griffs’ know that [...] the worst person to obtain advice from is the man who has been himself ‘let in’.
1864, 1867, 1870		Hotten Sl. Dict.
1866		Sportsman 9 Oct. 2/1: Notes on News [...] He is, by the way, a ‘lame duck.’ He accordingly has published a list of defaulters who have ‘let’ him ‘in’.
1881		N.Z. Observer (Auckland) 15 Jan. 169/3: The victim is a struggling Auckland boatbuilder, and he has been ‘let in’ to the tune of about £200.
1889		Music Hall & Theatre Rev. 4 May 184/1: They let me in for the whole of the rent.
1890		Bulletin (Sydney) 26 July 8/1: Mr. Gaunson. – They can’t come just now; they have finished skittles and are tossing for drinks with the Ministry. / Mr. Fink (Rushing in excitedly.) – Nebuchadnezzar! here’s a lark – Duncan is let in for the liquors!
1898		E.S. Mott Mingled Yarn 106: I should have probably been ‘let in’ for a considerable sum, through having backed the bill of a brother officer, who had to leave the regiment in a hurry.
1905		Sporting Times 18 Feb. 2/3: He had got let in awfully by an old Johnny who gave him rotten advice.
1920		‘M.M’ [Maurice Magnus] Memoirs of the Foreign Legion 282: [W]hen that stampede occurred at the outbreak of the war [...] I was let in for 350 dollars, and I don’t intend to be let in for another cent.