Depends on the cost and volume of the undercutting. If someone undercuts one or two of an item, I'll usually let my prices sit as they'll sell. If someone floods the market with an item, but only undercuts a hundred (or so) Gil, I'll undercut them by 50 Gil and let the stock sit. If undercut by a few hundred though, I pull my stock from the market board and let it sit in my retainer a few days to see the price goes back up. Although, in many cases, it stays at the undercut price because others see several of one item being flooded on the market and assume it must be selling really really well. It's the end result of people not using the history function or the history function only holding so many documented sales before the oldest disappear from existance.