Auctions & Trade (manual)
The Auction House is where you sell your extra items, or buy items from other players.
The basics of buying
Pick the category of item you're interested in (searching by item name will be available soon). Then pick the item you'd like to buy.
Items can be listed with a "buy-it-now" value. If they are, you can click the Buy Now button to purchase it immediately at the buyout price.
Alternately, you can bid on the item by putting the bid price in the box and hitting the Bid button. The auction house will take your money immediately and will hold it until either the item delists and you receive it, or someone else bids a larger amount, in which case you will get your money back.
Any item for which you are the top bidder will be highlighted in blue, just like the box surrounding this text. You will also see a note in the Notes column saying "(Top bidder)". Both of these clues will let you know that you currently have the item. The auction house will allow you to outbid yourself (if you feel you need to make a more competitive offer) so be careful not to accidentally bid against yourself.
The basics of selling
To sell an item you must pick which item you want to sell, the quantity of that item that you want to list, and then make some choices about the prices you want to set. You can set a starting price, which is a minimum bid that buyers have to meet before they can get the item. Note, however, that this starting price will be used to determine the listing fee of the auction, so an unrealistically high starting price might cost you money if the item doesn't sell. You can leave the starting price blank, in which case it will default to the autosell value of the item.
You can also enter a "Buy-it-now" price for the item. This is also optional. If you leave it off, bidding will simply continue for the duration of the auction. If you put in a buy-it-now price, other shoppers can purchase the item instantly at any time for that price.
Finally, you need to pick a duration. Currently, because of the beginner state of the economy, the choices are 1, 3, 12, and 24 hours. These will probably be shortened as more people join the game.
Any item which you have listed will show up in a gold-colored box, just like the box surrounding this text. You will also see a note in the Notes column saying "(Your auction)". Both of these clues will let you know the listing is yours, to prevent accidentally bidding on your own auction. The auction house will allow you to bid on your own auctions, but it's important to note that if you end up winning your own auction you will be charged the standard selling fee (see below).
Auction durations
Very short means around 15 minutes or less. Short means one hour or less. Medium means less than four hours. Long means 12 hours or less. Very long is any amount longer than that.
Selling fee
Every seller who lists an item is charged a listing fee, which is equal to 5% of the autosell value, or 5% of the starting price, whichever is higher. If the item sells, the seller gets this fee back, along with the proceeds from the item. If the item doesn't sell, the auction house keeps the fee. However, if the item does sell, the auction house retains 5% of the selling price.
Buyers never pay a fee for purchasing items.