Green’s Dictionary of Slang

roper n.2

also roper-in
[rope in v.]

1. [mid-19C–1960s] (US) a detective; also attrib.

2. [mid-19C+] that member of a confidence trick team who first meets and lures the victim into the plot.

3. [mid-19C+] (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.