Depending on how you play it, both are true.
It takes a lot of credits to perform crafting, specially if your like me and have bad luck. Namely cause to get the blue/purple schematics you have to create the previous 'version' (green and blue respectively) and reverse engineer it for a 20% chance (to clarify, that is 20% chance on each piece you create) to get the next 'level' in the chain. Plus, having to use the gathering skill to get the blue mat and having to critical in order to get he purple.
However, that is how you can make 'millions' by crafting: by crafting and selling the blue/purple products on the GTN. From what I've seen, this applies mostly to the 11 (lowest creditable mods) to 50(ish) levels. Sometimes, people do not want to wait to farm the Planetary Comms (or just don't have enough to do so) to upgrade themselves and their Companions in new mods (note, this applies to Cybertech, Artifice and to a lesser extent Armstech).
Same thing applies to Armormech/Synthweaving. You can make decent money, if priced right, selling 'lower level' equipment on the GTN. Namely blue/purple gear. Empty shell modable gear can also help make some profits, as everyone is looking for the right look for them and their chosen companion.
Biochem can be good, as they do make Implants, Stims and Medpacks. But the purples are only good for people WITH Biochem. But, the higher level Stims and such can still make some money.
Armstech is widely considered the least profitable crew skill (least as far as I know). Most of its modable craftings look horrible form what I've seen. Which leaves only Barrels to even attempt to make money with. A real gamble imho.
If you have the time and credits to spare, you CAN make money using the GTN for crafting skills. But, it just comes down to luck and what you put up for how much. It is VERY server dependent.