The game is still expanding. It has been mentioned as I have seen that the economy and the whole economical system is nothing more than barebones, so the game will have that in. It has not been worked or expanded and I am guessing that will happen only after the 4th inactive skill tree will come in the game.
For the Black Market, it is mentioned in the Starsector page that it goes hand in hand with normal market. You can make easy gain with commodities that can be bought low and sold high. FOr example one of my fav commodities being heavy machinery, they can be bought at as low as 40 and sold easily as high as 500. Of course at times you only find them for around 100, but also they can be sold at 900 at times.
If in the good chance you buy 1000 at 40 and sell them at 500, you will pay about 100000 and sell them for 250000. That is 150000 gain in the open market, where in the black market you could make about 200000 gain. Trading needs patience and at times, at least for me, buying large amounts of commodities at low prices, when there is no demand for them and stashing them in my base. When I see a really good price for that commodity, I run to my base, load the cargo and go to sell it.
By then the black market is not something you need to make a gain. The black market is there to make an much bigger gain. I will say this; In Ironclads the tax is 10%. Except if I am forced to sell in the black market, when the faction I will sell to hates me, I find no reason to sell in the black market. Making 900000 vs 1000000 is unimportant, when I reach that amount of money and I know I can repeat another good trade and make another 900000. But if it was 700000 vs 1000000, now that would make me try to sell it all in the black market and if I could not, I would sell 40% in the black market and then rest 60% in the opn market, trying to lower the loss.