Green’s Dictionary of Slang

1. an informer.

1606

P. Holland (trans.) Suetonius’s Historie of Twelve Caesars (1899) I 206: The false information of matters, whereof the penaltie came to the Exchequer, he repressed: and sharplie punished such Informers. And this (by mens saying) was a speech of his, 'The Prince that chastneth not Promoters, setteth them on to promote.'.

2. a confidence trickster.

1606		J. Day Ile of Guls III i: lis.: These are notable knavish courses. What breeding hast had? man.: Very good breeding sir: My great Grandfather was a Rat-catcher, my Grandsier a Hangman, my father a Promoter.
1617		Holyoake Dict. n.p.: A promotour, which, having part of the forfeit, bringeth men into trouble.
1938		A.J. Liebling ‘The Jollity Building’ Just Enough Liebling (2004) 257: The promoters, the fellows who are always trying to earn, in the local idiom, a soft dollar.
1950		Goldin et al. DAUL 164: Promote. 1. To swindle by high pressure means; to give, or use the promote. [...] Promoter. One who promotes.