Due to its geographical proximity to Starspire, Westcrown is a thriving port city.
Perhaps nowhere is this more evident than in the northern Thassalonian Ruins, which house the legendary Dusk Market; a wandering bazaar from which all manner of illegal goods and services can be purchased: drugs, slaves, poisons, alchemical crap Wundras forgot that he made, strange creatures, and prostitutes.
It is also said that Westcrown’s Underworld – and indeed, the city herself – is ruled from the shadows by a group known only as The Council of Thieves, a clandestine organization at least peripherally similar to Starspire’s Shadow Lodge, led by mercurial Grandmaster Torch.
It’s also possible that Westcrown simply wanted to play conspiratorial hipster, and say that they had a shadow government before it went all mainstream.
Regardless, next to Starspire itself, Westcrown is probably the best place in central Golarion to buy weird shit, due to its thriving grey markets.