Green’s Dictionary of Slang

1. to vacillate.

1805		J. Davis Post Captain (1813) 145: But this backing and filling is nonsense.
1846		Bell’s Life in Sydney 31 Oct. 3/1: After a good deal of ‘backing and filling,’ the captain being seated to the rear of the witness-box, whilst the mate was under cross examination.
1854		N.Y. Herald 15 June n.p.: There has been [too] much backing and filling, not only upon the Cuban question, but upon every other.
1899		H.E. Hamblen Yarn of Bucko Mate 198: Look here, colonel, [...] you know you refused our proposition ; don’t back and fill over that now, because it won’t go.
1915		C.J. Dennis ‘The Stoush O’ Day’ in Songs of a Sentimental Bloke 29: The champeen backs an’ fills, becos / ’E doesn’t feel the Boshter Bloke ’e was.
1924		C.J. Dennis ‘The Faltering Knight’ in Rose of Spadgers 19: But, all the same, ’e wouldn’t back an’ fill, / An’ argue with ’imself, an’ ’esitate.
1937		‘Red Collar Man’ ‘Chokey’ 81: An example of this ‘backing and filling’ is my recorded impressions of the jailers.
1963		R. McGregor-Hastie Compleat Migrant 105: Back and fill: to change your mind too often.

2. to charm a potential victim before subjecting them to a confidence trick.

1943		Baker ‘Influence of Amer. Sl. on Aus.’ in AS XVIII:4 253: The Sydney Telegraph of July 14, 1936, palmed off on the public as Americanisms current in Australia: [...] to back and fill.
1989		J. Morton Lowspeak.