IMO the real problem here isn't the market board itself but the fact that when listing items on your retainer you have no immediate means of checking other current listings. A lot of the massive 50% undercutting is coming from lazy players who don't bother to actually check the prices before listing and so use a random figure in their head... this is also why you frequently see listings of crafted goods at less than their material cost, because some people don't bother to check.

The supply and demand concept requires market stability to function properly, and when you have random people pricing goods using arbitrary numbers that have no relation to their actual value you have zero stability.