The trading system is not that interesting compared to what you do. The basics is always buy low where there is supply, sell high where there is demand.
It's more important how you place your local resources and production specialities as well as how you setup the mechanics of demand.
Patrician 3 is a brilliantly designed trading game and I recommend to everyone to at least look at the resource map.
Supply and production is pretty straightforward, but demand is more complex and can make or break your game. Patrician 3 is also great here with 3 population types with their own demand. It is also good if you can tie demand with city growth and development like in Anno 1404.
In a trading game it's all about the fight against the players optimum. There is couple of ways trading games solve this. The last thing you want is something that is too reliable that the player can do over and over again. Investments can work to reap bigger profits reliably but in that case the economy has to scale to play with the bigger boys and higher stakes.
Have multiple ships all over the world tackling multiple locations.
Have danger along the way that might make you reevaluate your plans like Storms or Super Strong enemy fleets that can kick your ass. It's also good to have this information beforehand otherwise the player will push his way on regardless.
In Patrician selling is incremental(or averaged out) so the more you sell the more you satisfy demand so its efficient to not sell in just one place leading to the creation of trade runs.
In Patrician it takes some time to "digest" what you sold so you have to do runs with other products.
In Patrician your competition is also selling stuff so information is important, you can setup information networks and you want to have backup plans by going on a route where you can sell in multiple places along the way.
An information network can really break your trade game so its best to balance it with recurring costs, like crew costs and taxes if you expand too much.
Supply/production and demand is generally known in one location but the current state might not be, you can make some informed choices based on time, previous information, your surroundings and predicting your competition.
In Starsector "economic disruptions" I think are a mistake since they tell you too bluntly what your opportunities are. But that is circumvented somewhat by the encounters while traveling there and having an awesome combat. Thus efficiency comes in the form of how good you are in combat.
In Starsector it does well the economy of scale well since you can invest in large ships that move cheaper product in larger volumes.
In X3 Albion/Terran the economy has "holes" that you can fill up investing in the relevant station/factory.
In X3 equipment can be directly used for outfitting your fleet so the economy is not useful only for monetary reason but also for your combat potential.
In The Guild 2 the items you make you can sell on the market, they also have functions that the competition can use. If you buy all the antidotes and then poison your competition then they cannot heal themselves.
In The Guild 2 business also have simple input output system for their product. If you can monopolize and control the input, like buying the input resources on the market, taking over the farms that generate the input and controlling the harvest points with thugs you can starve a business.
In Battle Brothers enemy forces can raid towns and target traders on the road that affect the economy of the surrounding towns. Similarly in Starsector you can target traders and blockade a planet or sector by blockading the wormholes.
In a more complex game you can do this also with the output where you can use the desirability of your output that you have cornered the market in for political advantage. In other words in a game with factions and useful equipment like in X3 you can sell to a particular faction to equip them and give them an advantage(note:this does not happen in X3 itself).
Offworld Trading Company also does this type of manipulations.
Interesting economic games: Patrician 3, X3 Terran/Albion, Starsector, Factorio, Imperialism Series, Battle Brothers, The Guild 2, Anno 1404, Cultures/Northland, Tropico, Offworld Trading Company, Space Run, Galaxy Trucker, Food Chain Magnate(not necessarily a good game).