You can obtain any item in WoW by going out and interacting with the game world. This can be questing, rep grinds, farming mobs, crafting or farming nodes. As people are by nature effort minimizers, this means you can get them to pay a premium for giving them easy access to what they need through the auction house.
This is what I base my entire gold making operation on.
Some examples of this effort minimizing behavior that you can take advantage of includes:
- Farmers posting their stuff below market to sell it quickly
- Overpaying to get the right amount in as few clicks as possible
- Paying a premium for crafted items you can't make yourself
- Posting lots of auctions with the standard UI is super hard so people won't do it
I will go more in-depth into these themes on my blog
and show they relate to the markets I am in and my approach. For the 4th one the obvious answer is to use TSM to minimize your effort in re-posting auctions.