Green’s Dictionary of Slang

gamdiddle v.

to cheat.

1899		A. Binstead Gal’s Gossip 57: The very next day the creature ‘gamdiddled’ (that was the coachman’s word) the stableman out of his corn money.
1910		Truth (Perth) 5 June 12/2: Well, them three got awful shikkered / Each and every one you see; / Two, because they’d been gamdiddled, / One, sir, out of sympathy.