Green’s Dictionary of Slang

1. (US) a detective; also attrib.

1869		N.Y. Times 22 May 2/1: Men and women engaged by us in the capacity of ‘shadows,’ ‘ropers,’ or general detectives.
1956		‘Ed Lacy’ Men from the Boys (1967) 91: Bill even pulls the roper line about he’s a witness, not a dick.

2. (US Und.) an employee of a dancehall, brothel or gambling house whose task was to entice passers-by into the establishment; some ropers worked from hotel lobbies, where they paid the clerk a fee to introduce them to wealthy or gullible tourists.

1840		N.O. Picayune 31 Oct. 2/3: He had not well landed on the Levee, so famous for cotton bags, sugar [...] ‘ropers in,’ and other ‘dry goods’ [DA].
1853		N.Y. Clipper 19 Nov. 3/6: Make yourselves known, next time, and possibly the getters up of these ‘innocent and instructive little games,’ such as ‘thimble rig’ [...] may ‘take you in,’ as ‘roper in’.
1859		Wkly Varieties (Boston, MA) 3 Sept. 5/2: We now caution the ‘ropers’ who hang around the Tremont House.
1865		Leaves from Diary of Celebrated Burglar 96/1: We found a few ‘pigeons’ and ‘ropers’ lolling around the room, but play had apparently not commenced.
1866		Night Side of N.Y. 62: It is now the function of the confidence man – who, in this branch of the business, is known as a ‘roper-in’ – to ascertain whether the stranger has any money about him.
1873		J. O’Connor Wanderings of a Vagabond 203: Johnny Chamberlain shortly became known amongst sharpers, as the best ‘roper-in’ in the city of St. Louis. [Ibid.] 204: By his audacity and energy as a roper, [he] gained the envy of all the sharpers throughout the West.
1874		‘A.P.’ [Arthur Pember] Mysteries and Miseries 52: With a view of testing the audacity of these ‘runners,’ or ‘ropers-in,’ I took the bull by the horns and accosted one of them.
1887		Lantern (N.O.) 27 Aug. 2: A good thing to kick them scalpers or ropers-in off the street.
1890		Sporting Times 15 Feb. 5/5: They are ropers pretty nearly to a man, and guinea-getters all round.
1910		Bulletin (Sydney) 13 Oct. 12: The Athletic Chucker-out and Roper-in: ‘Keep him going, missus, for a few minutes more. Then he’ll miss the bloomin’ ’bus and his cheque’ll be ours.’.
1911		G. Bronson-Howard Enemy to Society 111: I’ve got the keeper of the ‘rope house’ where he slept all that night; also three ‘ropers’ who remember him being there at twelve o’clock.
1927		Chi. Dly News 2 Aug. f.n. 2 in Illinois Association for Criminal Justice et al. Illinois Crime Survey (1929) 862: Cusick [...] is operating a disorderly hotel at 516 South Wabash Avenue. [...] Male ‘ropers’ on the street ballyhoo the place like a barker at a street carnival .
1937		‘Boxcar Bertha’ Sister of the Road (1975) 173: The ‘roper’ who stood in front and solicited business was Bad Eye, a tall, goofy kid of about twenty.
1938		(con. 1860s) H. Asbury Sucker’s Progress 415: A jostling mass of cappers, steerers, ropers-in and pickers-up, fighting over the suckers and literally dragging their prey into the gambling houses.
1940		H. Asbury Gangs of Chicago (2002) 73: In 1860, when he was about twenty-seven years old, he became a roper and capper for a small faro bank.

3. that member of a confidence trick team who first meets and lures the victim into the plot.

1866		H.L. Williams Gay Life in N.Y. 88: Loafers by day, and pimps, ‘ropers in,’ and thieves by night.
1881		Trumble Man Traps of N.Y. 10: Mr. ‘roper-in’ expects this. [...] his partner, ‘roper-in’ No. 2, or, as he is styled, the ‘catcher.’.
1895		C. Crowe Aus. Sl. Dict. 67: Roper-in, a confidence man who looks out for a victim at gaming.
1938		(con. late 19C) H. Asbury Sucker’s Progress 58: The Banco establishments employed large numbers of steerers and ropers-in.
1940		D. Maurer Big Con 11: Ropers to bring the victims in and an insideman to do the playing.
1951		D. Dressler Parole Chief 234: The roper, the first contact man, goes into a community to find a victim.
2014		New Yorker 17 Nov. 🌐 A theatrical fraud based in Switzerland that makes use of Montblanc fountain pens: Could there be anything more Cesar-like? I double-checked the roper’s age; it aligned perfectly with my ex-roommate’s.