Green’s Dictionary of Slang

roper n.2

also roper-in
[rope in v.]

1. (US) a detective; also attrib.

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

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

[US]H.L. Williams Gay Life in N.Y. 88: Loafers by day, and pimps, ‘ropers in,’ and thieves by night.
[US]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.’.
[US](con. late 19C) H. Asbury Sucker’s Progress 58: The Banco establishments employed large numbers of steerers and ropers-in.
[US]D. Maurer Big Con 11: Ropers to bring the victims in and an insideman to do the playing.
[US]D. Dressler Parole Chief 234: The roper, the first contact man, goes into a community to find a victim.
[US]New Yorker 17 Nov. [Internet] 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.

3. (US Und.) an employee of a dancehall 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.

[US]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].
[UK]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.
[US]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.
[US]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.
[US]Lantern (N.O.) 27 Aug. 2: A good thing to kick them scalpers or ropers-in off the street.
[UK]Sporting Times 15 Feb. 5/5: They are ropers pretty nearly to a man, and guinea-getters all round.
[Aus]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.’.
[US]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.
[US]‘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.
[US](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.
[US]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.