Keeping in mind that almost any reasonable buyer will take the cheapest option presented to them, undercutting itself is a logical move by any seller. Undercutting by a large margin is a strategy I sometimes will use if I notice that a certain high-value item sells very slowly at the "established" price. The items I make are very high-end most of the time; the pool of buyers is already very small, and if I want to make sales I need to clearly make my goods the best option. I'll normally sell >5% below the lowest set price so that mine will still be the cheapest even if the buyer pays market taxes. If the item is something I can easily make more of, selling volume at a discount will make me way more gil than holding out for a month hoping that all of the cheaper options will sell and mine will eventually get picked up at a higher price.