All through the slums, it's easy for the knowledgeable to find the underworld - or the ignorant to stumble into it. A place of shady bars, back alley trades where fixers make themselves a necessary evil giving people what they want. You can find arms dealers selling hot tech, back alley surgeons implanting illegal technology away from the prying eyes of the law.
The careless, arrogant or foolish will quickly find themselves taken for everything they have - either suckered into bad deals, or outright robbed. The savvy, who know what they want and have the cash to get it, can find anything.