Green’s Dictionary of Slang

fob n.

a trick, a deceit.

1622		J. Mabbe (trans.) Life of Guzman (1967) IV 136: Many men would deale more honestly [...] if these fobs and giggs were not put into their heads by others.
1660		Wandring Whore IV 8: He was forc’t to un-strip and leave his Gold Ring behind him, swearing he would be reveng’d of his Mob for putting such a fob upon him.
1672		Wycherley Love in a Wood I i: gripe: You are the Cup-board of Charity. joyner: You are the Fob of liberality.
c.1698		B.E. Dict. Canting Crew n.p.: Fob c. a cheat, trick.
1725		New Canting Dict. [as cit. c.1698].
1737, 1759, 1760, 1776		Bailey Universal Etym. Eng. Dict. [as cit. c.1698].
1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue n.p.: Fob, a cheat, trick, or contrivance, I will not be fobbed off so; I will not be thus deceived with false pretences.
1811		Lex. Balatronicum.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.

In compounds

fob action (n.)

an act of criminal trickery.

1747

H. Simms Life of Henry Simms/Alias Young Gentleman Harry 23: I was informed that M—m’s Wife was arrested in a Fob Action, and sent to a Spunging-House.

In phrases

come the fob on (v.)

(US) to cheat, to trick.

1848

‘Ned Buntline’ Mysteries and Miseries of N.Y. I 62: He come ze fob on some of ze nobilitie, and zey invite him to go to Amerique.