When I set out to build this game, trade was the most significant goal for gameplay. But what is trade?
The main game which inspired trade is Taipan! In this context trade was simple yet elegant, you could trade general goods, arms, silk and opium. The obvious goal of buy low sell high applied and there was very little strategy required. Randomly goods would be sold for incredibly low prices and other times the goods would sell for many times the average price. This was a great system for a simple game. Another game that did it well was Drugwars. Similar in nature but gave you a limited amount of time to make trades.
In the case of Taipan! the game was fun but only playable until you've reached the point where the game couldn't render how large your bank account became without using exponents. In the case of Drugwars, the game ended too quickly. But in both cases, there was the ability to shop around without costing more than time or a possible attack.
As I build this game out, there's a general theme that you will be able to stockpile a ton of goods in your ship and travel around to sell for the best price. The downsides include time to travel and cost of fuel to transport the goods around. In some cases goods will decay over time, so making quick trades is important.
But there are other ways to trade. What if you want to profit on goods that are sold without dealing in them at all? There's several paths.
Commodities markets will exist that allow you to trade in the form of stock. Buying and selling stock can be very profitable but also destroy your savings if you don't know when to escape a loss. You can also trade on indexes that pool many types of commodities together. The ability to make bets on the market in the form of futures also exists. But in some cases, futures can be the quickest way to drain your bank account if you make bad bets.
Professions also exist around trade. Delivery being a significant one. A typical ship can transport goods from one side of the galaxy to the other in about 4 hours. If you use shuttles instead of your own ship you can move around a little quicker if the shuttles are arriving and departing in your favor. But if you needed to transport some materials in just a few minutes, you would need to hire someone that specializes in high speed delivery. The ships used for this are very specialized and cannot be equipped for combat. Players that are very advanced in the delivery professions can do interesting things, like deliver a fleet of combat ships to a particular place in the galaxy.
You can also be a producer of goods without dealing with selling them at all. Should you decide to create a farm, mining outpost or factory, you can also join a trade federation that will pay you based on predetermined contracts. You won't get quite the same amount as if you sold it on your own but you won't have to trek around trying to make money on it either. You may still have the ability to take a portion and sell it on your own but depending how large you grow your operation, you may be focused more on the management of the installations and working more on profit per hour modifications and focus very little on the individual items you produce.
Similar to the above, you could run a trade federation and basically be a distributor or another way to view it, importer/exporter. The scale you choose to do this on has a lot of dependencies.
Another avenue of profit is running storage facilities. While many mining, farming and other installations will have their own warehouses, there will be times when traders need to stockpile large quantities of goods. Being in the position to provide ample security and protect against the decay rates of rare materials takes special skills acquired in the profession. Combined with delivery services, sometimes the fastest way to profit is by just providing services.
Finally, crafting will have significant impact on trade in the game. While the early phases of trade will focus largely on trading resources and commodities, player crafted items will end up being where the vast amount of wealth will be generated in trade. Everything in the universe can be crafted by players. Even planets but that's a different discussion topic. In some cases players may which to turn their small crafting operations into corporations and even have their stock traded on the markets.
The economy will be largely based on the main commodity markets. A planet's worth is based on the current supply of raw materials and its ability to purchase. This being the main thing to swing the markets. Players can have impacts on the markets but the bulk of the fluctuation in market prices will be non player entity driven. The concept being that while players make up the bulk of gameplay, NPCs outnumber players significantly.
As I stands, I've completed the creation of the main commodities. There are 6 classes and 35 different commodities in all. Within each commodity there are hundreds, if not thousands of possible options for trade. What this means is that a commodity class would be radioactive minerals and within that, there could be thousands of types of radioactive minerals. At the commodity market level, you are trading against the market shifts of all radioactive minerals but a miner may specialize in just a few and trade them specifically.