Welcome to free market + complete stupidity. You see it all the time with people who undercut by insane amounts. "Oh this has been selling forever for 50k? Ill sell it for 5k because DERP!" The best part about this is people who have no understanding of economics at all will argue that is how supply and demand works.

The trick to making money in FFXIV is basically the same as all other MMOs. Find something that makes a profit that you enjoy making/collecting and if someone screws up the market for that item get out of it and find a new one. I have never been broke in any MMO and I never focus on making money because I don't care about that stuff.