Sorry, the excuse that you're doing it for the buyers doesn't fly when the only thing that makes you help the buyers (tanking the prices) is someone undercutting, and you probably already undercut someone else to list your items in the first place. At least be honest and admit that this is born out of arrogance and selfcentrism because you can't handle someone else selling theirs before you. Where was the buyer friendly price in the first place when you listed your item, and why does it only come when someone just places their item 1 gil below yours and you decide to ruin it for everyone else selling that item.

Tldr: who died and made you white knight of the consumers, when your white knighting only comes out from hating that someone sells their item before yours and they're not even hurting your profit?