Trade links will only work in the trade channels. They will not work in other general channels.

Trading Channels

There are public trading channels located in the big cities. You can only use these channels while in the cities.

Find Out Who Uses the Item
Know which classes use which type of equipment:

Mail Armor: Warrior, Paladin
Leather Armor: Druid, Rogue, Shaman, Hunter

Cloth Armor: Mage, Warlock, Priest
Weapons: some items can only be used by certain classes

Trade Skill Components
Players with trade skills will pay money for stacks of normal and rare components, such as medium hide, 20 light leather, or a lesser moonstone. Ask around before selling these types of items to the merchants.
Making Deals
The goal of a seller is to get the best item or the most money for their item. The goal of a buyer is to try to get deals on items, and to get them as cheaply as possible. Prices are not fixed, so haggle. If the person won't go for the deal, chances are someone else will. If the person has a very valuable and rare item, you might have to give in to the seller's price if you really want to get the item. If you're having trouble selling your item, lower the price. Find out what an item is worth.

Figure out how rare it is and what people will pay for it. Look around and see what people are offering and are paying for items. Then come up with a price or offer a similar price. You can watch the sales of other similar items to find out what your item is worth. Item prices will change depending on the time of day, which determines how many players are on. There are also many other factors that can make an item more or less valuable.