What we need is anarchy systems with no black market who pay the same price for everything and in other systems where a black market exists it should discriminate on price to pay a lot less for what they produce, less for items they have no buy order for, more for what they need and a lot more for illegals.Stolen goods could be made more valuable while avoiding exploits by simply adding X credits to both the buy and sell value of every commodity. The profit margin for buying and selling them would remain the same, but being able to sell them without having bought them first would be much more lucrative.
The two downsides I can see are that newer players would have a harder time bankrolling an entry into trading, and being destroyed with a hold full of goods would become much more financially damaging. The first problem could probably be overcome by leaving some cheaper commodities in place, but giving them lower profit margins to discourage anybody but new players from dealing in them. I'm not sure the second problem is actually a problem at all, at least not once there's a karma system in place to discourage randomly destroying traders.
Edit: Actually, it would make mining much more profitable as well. But that could be handled by lowering asteroid yields to result in the same profit for a given amount of mining time.
So that agricultural station in a high population system selling food would be paying you next to nothing for fruit & veg, less than they would on the open market for ores they don't really need, but be paying more for those premium consumer items they have a buy order sitting on the main boards for hundreds of thousands but can't get filled and a lot more for the narcotics and such like.