Given that the game doesn't really provide a crash course in Market Board economics, it's understandable that a large group of players will not fully understand how market trends work, or that listing a price for higher doesn't mean that it will sell less often, (assuming that it's the correct price). I chock it up to some people being inept at using the market board properly, others being impatient for gil and needing it fast, or a small subset that is intentionally undercutting for...whatever reason. A very small subset of the population will be undercutting because they know the exact cost of a craft, and they realise that they still profit even when undercutting the lowest MB price at the time.

While undercutting may be annoying, it does become a convenience for those of us who can use the MB well enough to buy things low and sell them high. So I don't really complain unless the price is forced down to a vastly unreasonable amount, and there's a risk of it staying there.