My list of things to sell is almost always longer than the amount of slots I have with which to sell things. So I undercut by 1 gil unless the lowest price is something I can flip for a profit.

For the longest time I tried to be a "fair" seller, and just match lowest, only to watch someone else undercut by 1 gil and sell while I'm dying to reduce my load. So I've learned, and I continuously undercut by 1 gil. Sometimes I get someone that gets so upset that they drop their price by 50%... great, I buy their item, and sell them both at profit instead.

And for the items that are driven so low in price that it's not worth selling... I buy the whole lot of underpriced goods, desynth them, and sell the mats (and Fieldcrafts/Battlecrafts) for way more than the source items were, which puts me back at square one in terms of having too many things to sell and not enough slots for it.

I am always making money from the market in this game, with very little effort. 1 gil undercut just keeps that process moving as smoothly as possible.