The dark trades is an umbrella term for those professions and activities which involve providing goods and services which are illegal, particularly those involved with the creation of artificial monsters or gudgeons. It includes traffic in human corpses (corses), monsters both dead and alive, and body parts of both. Despite the high risks for those involved, the financial payoffs can be immense and even some of those in power, such as the Archduke of Brandenbrass, are involved to some degree in the dark trades.
In the trilogy several characters who are to some degree involved with the dark trades are the antagonists. This is reversed in the side story The Corsers' Hinge, in which the corser Bunting Faukes is the deuteragonist.
Poundinch's close association with the dark trades was first revealed when the Hogshead dropped anchor on the western bank of the River Humour the same night after passing Proud Sulking to make a trade with some corsers on shore. After they made the trade, both groups were attacked by an unnamed ettin. Poundinch was able to escape but a few of his crewmen were lost. Rossamünd Bookchild overheard Gibbon talking about the incident the following day before Poundinch appeared and warned his boatswain's mate to keep quiet about what had happened.