Also, sometimes (rarely, but worth looking) items are put on the GTN for a song. They can be re-sold for a huge increase.
Yes, this is another good way. It also sort of goes hand in hand with my post. When you are looking to sell your stacks of farmed items, look and see what others have listed things for. For instance if you are putting a pile of metal up and somebody has like 5 listings of stacks of 20 for 100 credits per item in the stack, and the next guy above him has his stacks at 200 per item, buy out all the stacks at 100 per item and re-list them for 150 per item and also put yours up for the same price. Once everything sells you've made even more profit. Also, when you put up gathering materials in stacks, don't put them up in big stacks. Do like 20 or 50 per stack. It makes your listings more appealing because the overall cost is lower and some people don't want a big stack of materials, they're just looking for a few. Basically the name of the game is to become the Walmart seller of the GTN.