Note: This article is about the Mists of Pandaria Beta. There is no guarantee that this functionality will exist in the live version of MoP.
The new pet battle system in Mists of Pandaria is going to be one of the most exciting new features for a lot of people; however, a potentially unintended consequence of the way it's currently implemented is that by selling pets on one realm that you bought on another realm, you will be able to transfer wealth between servers or factions. Orkchop wrote me an email that got me investigating:
All these pets are bound to your account, across all servers, across both factions, and can be sold. You can log on to your level 90 main, buy some pets, learn them, then log on to another server, create a level 1 and go sell those pets at auction. All without touching the neutral auction house and its fees.