I think there are far better games for market PvP such as EVE Online, Guild Wars, or Kingdom of Loathing. Making profit on the WoW AH was very formulaic (refining raw materials into the largest variety of items possible to maximize turnover - see JC shuffle), the best route was to find botters who would sell raw materials to you below market rates, and the huge number of shards made markets much less interesting.

Every action also required far too much clicking, which meant many people just used tools like autohotkey (cheats, although nobody ever got banned for them), and having to relist products constantly to beat minor undercuts was a terrible experience.

WoW AH is to virtual markets what hitting a pinata is to hitting something that fights back - it's simplicity makes it unrewarding.