I’ll warn you right from the start that this technique requires a little teamwork between you and a friend. The idea is that while some pets sell well on the Auction House the quickest to sell, and the rarest, tend to be pets from the other faction. I play Horde and when an Alliance pet (like an Owl) shows up on our Auction House it doesn’t usually last very long.
So there’s an opportunity here for any low level characters looking to make some money. The amounts you’ll make probably aren’t big enough for higher level players to worry with. If you’re still interested, here’s how I do this.
First, create a new character on the opposite faction. You can either grind this character out to make enough gold to start buying the more common pets or you can have someone donate the gold to you. Eventually you’ll have enough gold to start buying pets to sell.
Once you have a pet ready to sell you need to get it to your character on the other faction. This is where teamwork gets involved. You can’t send items through in-game mail to characters on the other faction so that is out. So you’ll need to use a neutral Auction House. The problem here is that you can’t buy things on the Auction House that another character on your account is selling.
The work around is simple but takes coordination. You need to list your pet on a neutral Auction House for a few pieces of copper and then have a friend with a Horde character purchase it right away before anyone else does. Then that friend can mail it in-game to your own Horde character and you’re good to go.