It could use a lot of depth, but some of that comes with tweaking the economy lottery in general.
Personal thoughts-
1. Not every pilot should have the same access to the black market. Just got his first ship squeaky shoes mc nice guy really shouldn't have tremendous black market contacts. I feel like rep/skills/conditions should all play a part in whats available in a black market.
2. Coming screaming on with full burn + transponder on reallllly shouldn't transition straight to me loading up guns, organs, drugs, and ships and streaking out again....maaaaaybe with a nasty letter(to say nothing of the planetary scans, resources, weapons, and ships i probably just dumped on the black market dock). Stealth already exists in the game as shown by the tutorial, and having the black market have more/better stuff because you went dark and slunk into a colony would really help give a payoff to fleets that care about sensor profile and the sneaky mobility skills/mods.
3. With those in mind, ideally, by default black market should probably always have the basics (supplies, crew, some trash weaponry). Skills and rep mostly determine what you can FIND in the black market. How you got into the port + ship mods like shielded hull should determine how risky it is to buy/sell some of those items. Landing on some random port as johnny mc nobody and waltzing over to the capital ship section of black market should maybe still be possible, but only on the understanding that you're going to be E burning your fleet out of the system with some VERY *** off locals (that said having them seize the stolen goods or force a fine should also be possible outcomes rather than just instant battle).
That may not be the perfect setup, but I think that this gives waay more interaction to the black market, and could make "smuggling" builds more interesting. As both selling and buying on the market now takes more skill, you can also increase the rewards. It gives a reason for you to up your rep with pirates as well, and should potentially lead to very powerful weaponry/ships, as another way to get them (main one being getting rep with a faction and joining, with the more common way currently being salvage).
Granted some of this is pretty intensive, so as a start, I think just tweaking what the market shows based on how you got into the system would help a lot. It may already do that, but i honestly can't remember since it's already "good enough" as is because a huge portion of what the market is used for is tariff free selling of goods. If you limit that (can only sell 5k worth or something if you come in blazing) I think you'll see a lot more players looking for less well defended worlds they can sneak into in order to offload their goods and maybe get better goodies.
Oh side thing-
TRANSPONDERS! It's a good idea, but there needs to be more to it. On and off is fine, but spoofing/veiling/something to temporarily allow you to approach a heavily guarded world in a "transponder off" state would be cool. Maybe have it be very short, require hacking a local node, and possibly a skill/hull mod (or any combination of these)