Your Brain.
Anyone who wants to learn to play the auction house in World of Warcraft can do it. Some players think that add-ons are required. Not a single add-on is required to be a lucrative auction house merchant. Add-ons only make things easier. If you are new and starting out on the auction house you don't have to download a single add-on. In my opinion, you will get a much deeper and better understanding of the auction house if you do not use any add-ons at all.
Granted, add-ons do make things much easier and faster, but they can also cause problems. Some players will set up traps that are meant to trick the add-on and its autopricing. Inexperienced auctioneers may fall for these devious traps and lose out on a lot of gold.
In my opinion, add-ons should only be added to make tasks easier or more efficient. I recommend building off of what you learn without add-ons, then add a few add-ons. When you have grasped how those work, maybe add a few more as required. Never let go of the knowledge you learn from playing the auction house, studying it, and manipulating it without the help of any add-ons. When you can master the auction house with your brain power, you will exercise your mind and strengthen your ability to both analyze and comprehend.
The number one add-on that you will need to use is your BRAIN.
All of the data that an add-on creates is based off of the same information that your brain has access to by simply viewing the auction house and cross referencing the prices. Add-ons can't tell you when it is time to bail out of a market or what item to stock up on for the next big patch. An add-on won't be able to tell you whether to learn or flip that rare pattern. Nor will it be able to decide which recipe to learn first. Add-ons aren't required to be a successful auction house tycoon. You will still be required to make many decisions in your auction house tradings. So exercise your mind's power.
For The Record: I use Postal, AnnounceIt, Auctioneer, and Gatherer.
