Green’s Dictionary of Slang

1. a pimp [? string of prostitutes/string n. (9)].

c.1607		Beaumont & Fletcher Knight of the Burning Pestle I i: A whoreson tyrant has ben an old stringer in’s daies, I warrant him.
1999		Guardian Friday Rev. 11 June 14: I play a drug-addicted crackhead stringer who’s a rent boy.

2. (UK Und.) a confidence trickster, a swindler [string n. (2)].

1821		W.T. Moncrieff Tom and Jerry III iii: You’re an out and out Stringer, you are!
1845		J. Lindridge Sixteen-String Jack 124: The dashy, splashy, leary little stringer, / Mounted his roan, and took the— Phililoo!

3. a hoax, a trick [string n. (2)].

1851		‘Pertaters and Ternups’ in Burke Polly Peablossom’s Wedding 89: As ready to hoax a friend as a stranger, he never lacked assistance [...] whenever he had concocted a ‘stringer’.
1926		Maines & Grant Wise-crack Dict. 14/1: Stringer – Big touch on a victim.

4. (N.Z.) a woman who works in a public house or bar encouraging the patrons to drink [string (along) v. (1b)].

1881

A. Bathgate Waitaruna 142: A barmaid in one of its hotels [...] is popularly known as ‘Goodall’s stringer’ [...] She makes herself agreeable to those who frequent the house, and so she ‘strings them on’ and induces them to spend their money there .