I liked the old way it worked in FE2/FFE for establishing "trust"
- black market contacts show up everywhere, though aren't always available
- about half of them are fakes
- you can tell which ones are fakes because they change their names regularly (after people get caught and mention it's a honeypot), whereas the real ones are more consistent
So if you know the area, you can find the real contacts easily enough. If you're new, you're going to have to either pay attention for a bit, or pick one and hope you get lucky.
There should probably be reputation checks involved as the black marketeers should be concerned that you working for the cops.
Reputation with who is the tricky bit.
- it would be weird for it to be the controlling faction, since black market trades normally hurt them
- there's no guarantee the system contains any Anarchy/Criminal factions (especially with colonisation where they're very vulnerable to being retreated)
I would think that having a notorious level of 5 or thereabouts might be a reasonable prerequisite for a black market to negotiate.
Seems a bit odd that smuggling (which isn't even a bounty-level offence!) would require you to first commit a bunch of serious bounty-level offences. Those seem like the sort of things you'd do when the smuggling job went
wrong.