here are numerous ways to earn credits in the game; which includes the quests, missions and tasks provided by the wealthy players.
One of the major sources of earning is the Galactic Trade Network; buyers and sellers contact each-other and then trade with their requirements. This might not be a very quick method, but once you get some experience; you will enjoy it.
For more help on SWTOR, read our Legacy Character Perks, Augment Slots and Credits Farming Guide.
The Pricing Strategy!
One of the important factors in the market is the force of the price. Everybody puts a little higher than that of his total expenditures on the production of an item. Sometimes, to beat the other sellers one might put on a lower price to get more buyers.
Every seller does it until he is rich already or has other means of earning. You should be sure that your price is not affecting the market's state as it may harm the general market.
Long run producers know that a big cut in the price is not very useful and not worth the time. Your cuts should not be more then 5-7%, and you should keep it in mind that other sellers are there too. You may make a lot of profit or might have to bare a lot of loss.