First of all this would be a guide in english from a german guySo please don't cry about school-english
What you need:
1. 1 lvl 90 Char.
2. Some Low-Levels on diffrent Servers.
3. 20.000 Gold to get started.
The Guide:
First of all get all characters to a majorcity with an AH. Now Search the auctions for some rar or epic pets.
Notice all the buyout prices and switch to your toons on the other servers.
Campare the buyout's and find some pets that have a mutch higher buyout than the others you have noticed.
Mostly you will find Level 1 pets - this is good for your strategy!
Next log back on your main and buyout the pets witch you can sell on other realm for a higher buyout. Lern the pets you buy and train them a little bit. As more level they have, then more gold you get
Now log on the twink, that is on the realm you want to sell the pet. Right klick in the petbrowser and put it in a box. Sell it and get the profit!
Notice:
I've made a lot of Gold with this and have learned that you better buy Pets that sell fast ( costs mostly 500 - 3000G), train then and then resell
Soo, have a nice day!