Green’s Dictionary of Slang

bob n.2

[? 15C–17C SE give someone the bob, to cheat, to trick]

a shoplifter’s assistant, to whom the stolen goods are quickly passed by the actual lifter; 20C use refers to any shoplifter.

Wandring Whores Complaint 5: The tenth is a Shop-lift that carries a Bob, / When he ranges the City the Shops for to rob.
[UK]‘L.B.’ New Academy of Complements 204: The tenth is a Shop-lift that carries a Bob, / When he ranges the City the Shops for to rob.
[UK]B.E. Dict. Canting Crew.
[UK]A. Smith Lives of Most Notorious Highway-men, etc. (1926) 203: Bob, a shoplift’s comrade, assistant, or receiver.
[UK]New Canting Dict.
[UK]Bailey Universal Etym. Eng. Dict. [as cit. 1725].
[UK]Scoundrel’s Dict.
[UK]Grose Classical Dict. of the Vulgar Tongue.
[UK]Lex. Balatronicum.
[UK]B.M. Carew Life and Adventures.
[UK]Egan Grose’s Classical Dict. of the Vulgar Tongue.
[UK]G. Kent Modern Flash Dict.
[UK]Flash Dict. in Sinks of London Laid Open.
[US]Matsell Vocabulum.
[US]Trumble Sl. Dict. (1890).
[US] ‘Jargon of the Und.’ in DN V 439: Bob, A shoplifter.
[US]Irwin Amer. Tramp and Und. Sl. 32: Bob. – A shoplifter. One of these individuals has declared that the manner in which he and his kind ‘bobbed’ in and out of a crowd looking for an opportunity to pilfer gave raise to the word; certainly the origin is no more far-fetched than many another underworld idea.
[US]Monteleone Criminal Sl. (rev. edn) 29: bob A shoplifter.