Green’s Dictionary of Slang

(gay) used of someone involved in commercial sex.

1937		J.M. Cain Serenade (1985) 16: It hadn’t occured to me up to that second that she could be a downright piece of trade goods.
1949		‘Swasarnt Nerf’ et al. Gay Girl’s Guide 38: ‘Gay Trade’ can really refer either to someone who makes no bones about being queer, but is simply against cocksucking, or to someone who considers himself basically straight, but enjoys a little kissing before he gets ‘blown.’.
1959		K. Williams Diaries 13 Jul. 153: Made a trade friend and reconnoitred. V. interesting.
1985		K. Vacha Quiet Fire 60: He would give me a blow job. This was a totally one-sided thing. I was trade, totally trade. No neckin’ or nothin’. And he was satisfied. [Ibid.] 61: I was still what they called ‘gay trade.’.