Selling items is more than supply and demand. More than marketing trends based on current and past behaviors. You have to realize that your consumers are human. That is to say today 80% may want to glamour their gear but next week they could care less for the rest of the games life time. The only things that are sure to sell on the market board unless crafters decide to level gathering classes is crystals in all forms. Even gear isn't a sure thing anymore as I am as certain as the sun rising every FC has at least one person with all crafting classes maxed leveled if not melded to the brim.
You cannot mistake wants and needs as being the same when it comes to marketing otherwise you'll be waiting on something that'll sit there for months. I need to eat. I need to sleep, etc. I want to play this game as much as I can but it will not pay my bills nor feed my family. In much the same way in this game people want to look great, they want their house to be the best. But will it make them better geared? Will their crafting classes be able to make 3 star items? Can they make the items or gather the items needed for their FC's goal furthering? Ifrit's Horn makes a nice piece of furniture to show off but it does nothing to further progression. Nor does it warrant a price tag of 900k much less 1 mil. Priorities always win out unless you have it to burn. That's how supply and demand really works.