Now that you know to loot everything (see tip #1), you’ll have a lot of items in your bags. Any item that is white quality or greater may sell on the Auction House. How do you know what will sell well on the auction house? Trade goods and green quality (or better) items will almost always sell on the Auction House. See our Auction House guide (coming soon!) for more information.
An advice for those who are trying to compete monopolizers: you cannot beat them by selling for less if they follow right steps. You should do opposite: sell for more. Because market will come down if the price goes unreasonably high. You can set a bid on item for the price it should cost and buy out price for higher than a monopolizer is selling. So, common buyer may get an item for the right price or monopolizer has to buy the item at his loss.