Green’s Dictionary of Slang

(US) an honest, dependable, trustworthy person; thus straight-shooting adj.

1920		T.A. Dorgan in Zwilling TAD Lex. (1993) 79: He’s two weeks behind in his bills here right now — I gotta idea that he ain’t a straight shooter.
1920		R. Hughes in Harper’s Pictorial Library of the World War X ix: Sergeant York was a straight-shooting open-living mountaineer.
1927		(con. 1917) J. Stevens Mattock 232: Mattock, you used to be a regular white guy, one of the real hard-boiled, straight-shootin’ babies of old Company F.
1927		W.R. Morse ‘Stanford Expressions’ in AS II:6 278: straight shooter—reliable.
1939		P. Cheyney Don’t Get Me Wrong (1956) 93: She’s lookin’ for a real man who’s a straight shooter.
1949		R. Service ‘Montreal Maree’ in Songs of a Sun Lover (1955) 72: But of straight-shootin’ Dawson dames, Maree was rated queen.
1953		C. Brossard Bold Saboteurs (1971) 295: Now you have a chance to live like an honest-to-goodness, four-square, straight-shooting true blue rat.
1955		B. Schulberg On the Waterfront (1964) 144: Johnny was Number One [...] a straight shooter.
1968–70		Current Sl. III–IV (Cumulation Issue).
1978		T. O’Brien Going After Cacciato (1980) 131: You’re a fine lad [...] a straight-shooter.
1997		T. Winton Lockie Leonard, Legend (1998) 34: Your mum’s a straight shooter, you know that.
2005		P. Howard Curious Incident of the Dog in the Nightdress 19: She’s a straight shooter, there’s no doubt about that.
2008		R. Price Lush Life 354: Berkowitz was about as straight a shooter as you could be for someone in his position .
2012		L. Berney Whiplash River [ebook] ‘He was always a guy, he’d look you in the eye he had something to tell you. He’s a straight shooter’.