Trade

To trade can have two meanings in GuildWars:

Trade with an NPC Trader
In all cities you can find Traders for various goods (runes, dye, materials, ...).

A trader, unlike a merchant or a crafter, does not sell and buy goods at a fixed price, but depending on supply and demand. You may even find a trader "out of stock" if there is very little supply.

Prices have a lower limit (the same price that you would get if you sell the same good to a merchant, but are open end.

Trade with an other Player
If you click an other human player while in an outpost or city the "Trade" button will appear next to his name in your target monitor. Clicking that button will start a trading session.

During a trading session you can offer any item you have in your inventory. You submit the offer and the other player will send back his offer in gold or items. Both sides can modify and re-submit their offers until they make the deal or cancel the session.

Beware of scammers while trading with other players!