I'd point out that when these undercutters come along, a lot of the time what happens is that other crafters/sellers snap them up and relist at normal price. There are several of us on our FC who do this on higher demand items all the time when the lazy start undercutting stuff to oblivion. Im sure the same calls of "plebs have tanked this market, buy em while their stupid cheap and make a profit" happens in every FC with crafters in it.
That the stocks sell same to next day or two shows these people arent engaging in supply / demand but more don't understand the market.