Most of the players make the mistake of only listing 30-50 transmog items on the auction house and then hoping to get half of them sold until the next day. Me and a lot of other gold farmers and transmog sellers do have 3.000-10.000 items on the auction house across various realms. It does not mean you have to do it that way – but if you have 1000 items listed, chances are higher you can sell up to 10 per day. With only 100 items listed, you have to be lucky to sell one. Of course, the sells are not guaranteed if you post more items. But i’m sure you have a lot more fun if you open your mailbox and 10-20 items are sold
Keep in mind that these quests are optional, and are not necessary to continue leveling and capturing companions. They are also account-wide, so if you complete the quest chain on one character, you will not be able to complete it again on another. However, any progress that you've made will be saved and you can pick up where you left off in the quest chain on another character. The dailies that you've unlocked will also be accessible by all your toons.
Now that you have these addons, it is time to set them up properly to be used as effectively as possible. With the first addon listed, Auctionator, you will get three additional tabs when you open up the auction house: buy, sell, and more. Buy and sell are easy to follow and read, the primary reason why this addon is the top choice and listed as number 1. You can easily set how much to buy or sell, ranging from 1 individual object to stacks of the same good. The most important way to search is by price per individual item. This will avoid both overpaying and underselling, since you can see what one item in a stack is worth compared to what it is worth when being sold on its own. The "more" feature provides an easy-to-follow window of all your auctions up and the details associated with your auction, such as price and time left, in a nice color coded fashion. Without this addon, you will be severely crippled compared to anyone using this efficiently. If you are afraid of addons for security reasons, the rest can be ignored as long as you have Auctionator!
The most simple thing is TradeSkillMaster. This AddOn shows you quite an amount of information in the items tooltip. In my opinion, DBRegionMarketAvg the best source. It tells me the price, an item was posted on all EU realms in the last 14 days. Why not DBMarket? DBMarket only shows you the items value from your server in the last 14 days. This value often gets manipulated. Some people start to post an item with a 500g value for 500.000 Gold on the auction house for several weaks. As a consequence, DBMarket is rising towards 500.000 Gold. If you use DBMarket with 100% and post your item for 500.000 Gold, nobody will buy it.