In World of Warcraft®: Battle for Azeroth™, the seventh expansion to Blizzard Entertainment’s acclaimed massively multiplayer online role-playing game, the fall of the Burning Legion sets off a series of disastrous incidents that reignites the conflict at the heart of the Warcraft® saga. As a new age of warfare begins, Azeroth’s heroes must set out on a journey to recruit new allies, race to claim the world’s mightiest resources in order to turn the tides of war, and fight on several fronts to determine whether the Horde or Alliance will lead Azeroth into its uncertain future.
Be warned that players will occasionally list items in the Auction House that are sold by vendors. This typically applies to limited sale quantity items or items in remote, harder to reach locations. Items from Outland that advance certain skills (such as books for training Cooking or First Aid past a skill of 300) are typical. These items are notoriously listed for 2, 3, or even 10 times their vendor purchase-able price. Using an add-on such as Auctioneer Advanced can forewarn you of such a tactic. You should ONLY buy such items if your server is so full and busy that you simply are unable to acquire the item on your own. Otherwise, wait for the vendor to re-stock (usually takes about 20 minutes to 1 hour depending upon the vendor). You'll save yourself a considerable amount of money. See Buying Items from Vendors for Resale below for more on this.
Anything that can be answered by reading the recent discussions on the subreddit, has a yes/no response or can be looked up on sites in the community resources should not be posted in a thread of its own. Questions such as 'What is this worth?', 'Did I make a mistake?', 'What do I do with XYZ?' or 'Should I buy/sell this?' will be directed to the Daily Questions sticky.
If you can Solo an instance, you have two options. The first is to take the place apart yourself and sell all the drops on the Auction House. For level 80 characters, Scarlet Monastery, Uldaman, and other mid-level instances are easily soloable, and are a very popular source of cloth and marketable blue and green items. If you're reasonably well-geared, and feeling more adventurous, Scholomance and Stratholme are also soloable, and can be extremely lucrative as a source of auctionable items.
Even if you don’t have flying in WoD be sure to get the WoD handy notes. If you have flying simply fly and pick up all the treasures that you can and do bonus objectives. Not every single piece of treasure will be worth it though as some are hidden in caves or are just hard to get. So if you find yourself spending more than a few minutes finding a treasure, just skip it and move on, there is plenty of treasure to go around.
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.