If I see it is one person, or two retainers that keep undercutting me by 1 gil when I list something, I just keep relisting it, let them undercut me to make sure they are watching the markets, then I will cut anywhere from 1k-20k gil in one jump, let them undercut me, watch for theirs sell, or even buy theirs, then relist everything at the original price. Or if it is a name I recognize as someone that constantly undercuts by 1 gil, I will undercut by thousands just to piss them off, it's not like money is worth anything in this game, but making those type people mad helps me sleep at night.