Being a normal merchant is not viable way to make money or grow in this game.
I have $2mil that says you're wrong. There is definitely good money to be made on pure, 0 mission trade and a small amount of cash can grow very quickly. It's not the best option in the world but it is absolutely viable.
The economy tracking system isn't pretty. From what I can tell, there's no strategic market tracker so the only way to locate trade demand is to Noah's Ark a single unit of every trade good in your inventory at all times. Not all areas of space have remote price data (I can't find clear indicators of trade beacons), and each beacon may track different planets as well. Whip out the pencil/paper because you'll be running half a dozen separate trade routes at once, buying up cheap goods when they're available and slam dunking 1-2 things when you find big money buyers.
Obviously you should trade everything on the black market, or the 30% tariff will murder you. When buying over the black market limit, get the cheapest items from the public market first to minimize the tariff penalty. Then load up on black market goods to avoid tariffs.
The best trade goods are obviously the illegal things. Marines can easily double your investment (beware the $20/month salary!) and heavy machinery has extremely good margins in small numbers. Ordinary supplies can do all right. Always keep an eye out for "demand" and "surplus" bargains, but be careful that not all factions will pay top dollar. Anything less than 50$ profit per cargo is a waste of fuel, but it's better to trade something than fly with an empty cargo hold. If a big organ buyer also needs supplies and fuel, do it all to make the most of the trip.
There will be far fewer trade missions on the map because you'll be doing them all ahead of time, which is a shame because they always give excellent deals.
