I undercut drastically sometimes simply because I felt like it. Some days I'm grumpy. Some days I'm feeling whimsical. Some days I just like round numbers. There's no rules against it, and I feel like I am just making items more accessible to more players. Somehow I'm still making money, so I have no reason to become more 'efficient'.

One time an angry competitor messaged me repeatedly and accused me of being a bot. They sent their FC mates to stalk me as well - 'trying to catch me in the act'. I reported them for harrassment and haven't heard from them since. People take the MB way too seriously. Last I checked, the Marketboard isn't the focus of the game.