Green’s Dictionary of Slang

square-shooting adj.

(US) honest.

1930		R.E. Howard ‘Waterfront Fists’ Fight Stories Sept. 🌐 She’s a peach, as well as bein’ a square-shootin’—.
1933		W.R. Burnett Dark Hazard (1934) 66: There’s an A-number-one, square-shooting guy sitting right there.
1935		(con. 1920s) J.T. Farrell Judgement Day in Studs Lonigan (1936) 803: Paddy Lonigan’s a square-shooting man with a heart of gold.
1972		T. O’Brien If I Die in a Combat Zone (1980) 71: Alpha’s a good square-shooting company.