Trading is a great way to make money.
Tips & Tricks
If you're new, and you're killing Space Eels or Space Eel Mothers, try selling the Ferrous Metal and Light Metal they drop as loot to a Light Foundry if it is buying it will surely make you some friends. Especially Ferrous Metal is in short supply and needed for upgrading buildings.
Harvesting Nebula Gas or Hydrogen Gas to sell to planets are also good ways to quickly get money early on, as well as selling bulk goods to planets.
For most goods, selling exactly 1 tick worth of goods yields the best results.
For example if a planet requires 374 light ore, selling more than 374 tons of it will earn you far less money than if you sold it just what it needed. There's exceptions to this; things like Hydrogen Gas, Nebula Gas and Water you can stock for many ticks, as a way to get the Upkeep Factor up.
A planet can hold 10 ticks worth of stock. If it is brought up over this amount either by an other planet tick while it is full up, or by players selling the goods to it, it will be removed at the next planet tick, and set to 10 ticks worth again.
This is also true if a planet loses population, resulting in a lower capacity for goods.
Planets currently have a maximum population. For M-class planets that limit appears to be at ~1.000.000 population.
Planet Growth & the Upkeep Factor
Overstocking counts towards the Upkeep Factor. So if you can't find the things a planet wants, (greatly) overstocking it with cheap easily attainable things like or can get that Upkeep Factor above 1.0.
As long as a planet's Upkeep Factor is above 0.5 it will recieve an increase in population, though the maximum population gain is achieved at Upkeep Factor 1.0, you can raise it further than 1.0.
At higher populations, an overcrowding becomes an issue. Larger planets will grow less, and will eventually stop growing.
There is also a random factor in the planet growth formula, so you could see some unexpected growth patterns if you pay attention.
BUILDING TRADE INFO GOES HERE
The Planet list may be useful for helping you find the closest planet of a certain class, or for seeing the planet-type balance of each cluster.