Patch after patch people come on complaining about undercutting because their item is listed at much lower then it was before. It has nothing to do with the market board system, it has to do with radical shift in the demand (or supply) of the product either up or down. With increasing ilvl and new recipes, the market for so many items basically resets each patch. There will be many gripes about why x item isn't worth as much or is now too expensive. Take any price history from last week with a grain of salt.