Depends on the material. On Harbigner, I've noticed that the luxury fabrics via underworld trading are horribly underpriced on the GTN, so you won't get good prices for them.
Similar things seem to happen w/sliced tech parts via slicing. There are periods where they're being sold for ridiculously low prices (as in, if someone bought them the seller would still be losing money) so you might have trouble selling those too. I did buy up the ultra-cheap ones a few weeks ago and have been selling them for the default cost, but it's going slowly because people keep selling them ultra-cheap.
Slicing parts aren't any good except the max level purple slicing parts. I have hundreds of slicing parts and I assume people who are dumping them on gtm are probably only running missions for the purple parts. That's why the blue level slicing parts are cheap. The purple slicing parts aren't worth buying since if you do that math comes out about the same cost of buying an already made lvl 49 augment. However, some player may only need like 1 purple part and don't want to wait on slicing mission to get one. Thus, the reason purple slicing parts have a high price.