Green’s Dictionary of Slang

half set n.

[presumably from set n.1 (2), with SE half indicating the dissatisfaction]

(mainly drugs) an unacceptable offer, usu. in the context of a drug deal.

[US] in D. Goines Cry Revenge 44: You goin’ to think that maybe I’m some kind of funky dude who’s out for a half-set .