Many people when selling products on the Auction House only focus on selling big ticket items or epic quality gear. While it is a fair way to make gold it leaves you restricted if your margins shift or collapse. The way to avoid this is by selling Rare and Uncommon items too diversifying your product range.
Good examples of this are the leg armours you can make with a Leatherworker, and gems with your Jewelcrafter.
So while your scanning and listing don’t forget to check the Rare and Uncommon markets, don’t forget the WotLK, or BC items too these items will sell to levellers.