even if SE bans them selling 40 slots worth of mats add up to alot of gil quick.
5k a stack x 40 slot = 1 million a day and imagine how many more accounts they have selling & farming. bans mean nothing to them there making big money from all the people buying from them they can just buy or steal new accounts without dipping into there pocket.
i dont bother undercutting i set my price it sells a few days later, im not going to just throw away what im selling.
longer they wait to ban the more damage is done.