The bazaar resells equipment and reagents sold by other players. Some items are always there (100) because they are not in demand and more people sell them then buy them. Other items are in high demand and are bought more often then they are sold. The prices also fluctuate depending on how many of that item are in stock at the bazaar. So if there is only 1 item available for sale it will cost more than if there were 25 available for sale.
Some players stay at the bazaar and constantly "refresh" the screen waiting for rare objects to be sold; because of this items like Golden Pearls, Sunstones, and Elucidate treasure cards are bought up almost as fast as they are sold.
This might be a glitch, but in Wizard City's Bazaar different ingredients, or Amulets are either different prices or not available at different times.
its because people sell stuff and depending on how many there are the price there changes based on how many or how less if that item there is at the bazaar and when its not there they all got bought of that item and nobody sold that item there yet