Green’s Dictionary of Slang

a casino employee who checks on the activities of the house players.

1730		Derby Mercury 14 Jan. 3/1: ‘List of Officers attached to Gaming-houses’ [...] 4. Two Puffs, who have Money given them to decoy others to play [...] 6. A Squib is a Puff of a lower rank, who serves at half Salary, while he is learning to deal.
1797		Sporting Mag. Sept. X 311/2: [as cit. 1730].
1804		Sporting Mag. May XXIV 125/1: [as cit. 1730].
1884		(con. 1731) A. Griffiths Chronicles of Newgate 208: A squib, who were spies upon the straight dealings of the puffs.