Green’s Dictionary of Slang

a cheater, a swindler.

1936		‘N. Bell’ Crocus 235: Oh, he didn’t diddle me [...] I knew him for a swizzler from the word go. It was his mistake .
1954		A. Buckeridge According to Jennings (1991) 141: You’re a bogus, gruesome swizzler and you haven’t a leg to stand on.
a.1985		‘The Open Book’ in G. Logsdon Whorehouse Bells Were Ringing (1995) 112: The sap sucking swizzler and cunt cheating chiseler, / of the barrel he’s only the bung.