Really, the vendor is just there to make sure something that is considered a base mechanic of how inscription is supposed to work, that ability to swap out glyphs, doesn't become massively overpriced. Even if the in game economy exploded, it still couldn't cost a player more than what they would get for selling a couple greens at 85. Would rather have that then have someone try to monopolize them right when I needed one and have to wait until someone undercuts their insane price of 200g. Laugh, but you've all seen this happen with items that people regularly use once in a while, I'm sure.