Trading is not a rare thing in online worlds such as World of Warcraft. Players who wish to level up their characters have long huddled with merchants and NPCs to get whatever they needed. Items range from those needed to survive a major boss to those that’ll score more kills in PvP.
But like any market, there are some rules to be followed in order to avoid any misunderstandings and even theft from other traders. And while these rules are meant only to ensure more enjoyment in the game (and more money from its paying players), such goals are not too far off from the goals of real-world marketing.