I usually do the opposite. I don't undercut stuff that doesn't get outdated, and I don't mind if they get sold in 1 minute or 1 year. I always end up selling them and getting full profit, instead of an undercutted profit. In the end you get more gil for the same, instead of farming/crafting the triple and wasting time.

I only undercut stuff that gets outdated fast, like a new minion that everybody wants right now, or new raid food/potions etc... and I always undercut them 1 gil only, because I don't want to break the market.