Prices are what players have paid each other at the Marketplaces, before shipping. An item’s guide price is the middle price of its sales over the last seven days, counted by the item, once it has had at least five sales between three or more players. Sales between one player’s own characters, staff’s sales, and sales flagged as suspicious (far above what an item is worth, or coins passed back and forth between two players) don’t count. What shops pay is for the first one: a shop pays less for each of something it has bought lately. Prices are worked out again every five minutes; what’s for sale is as it is now. Nobody can see who bought or sold.