Green’s Dictionary of Slang

1. (US) one who plays for time until a fellow-diner or drinker picks up a bill.

1922

Appleton Post-Crescent (WI) 3 May 7/4: Flapper Dictionary finagler – A person who stalls until someone else pays the bill.

2. a trickster.

c.1935		‘Betty Boop in “Flesh”’ [comic strip] in B. Adelman Tijuana Bibles (1997) 30: What an old phenogler this mug turned out to be.
1944		C.B. Davis Rebellion of Leo McGuire (1953) 165: He was a finagler and we just out-finagled him.
2004		J. Ellroy ‘Hot-Prowl Rape-O’ in Destination: Morgue! (2004) 265: Still a stud. Still a fast-track finagler.