Green’s Dictionary of Slang

(US) corrupted, susceptible to bribery.

1939		Howsley Argot: Dict. of Und. Sl.
1998		(con. 1986) G. Pelecanos Sweet Forever 260: [I] don’t want those sold-out cops you got in your pocket anywhere near my shop.
2001		G. Pelecanos Right As Rain 269: Ain’t nothin’ I hate worse than a sold-out cop.