Money making?

So i have been looking for a money making guide and i bumped on to this topic: Guide for beginners.
and it said there that if you got any t4 stones u can sell them for a nice price but when i tried it it gives u much less money than what the person said in topic...
What my question is did the price of T4 stones drop?
Or did that person lie?

In that guide s/he said to vendor, as in you open up your personal shop. Not sell to npc.