From:guildwars.com

It is our goal to provide an enjoyable experience to every Guild Wars player. That's why we take the topic of real-money trading (buying and selling gold or in-game items for real-world money) very seriously. Every week, we ban thousands of accounts used by real-money trading companies, because those companies harm the game for other players by running large networks of bots to farm gold and items, spamming chat channels with their advertisements, and even attempting to steal login credentials from unsuspecting players.

Why we crack down on real-money trading

Real-money trading and related activities such as botting and spamming are breaches of the User Agreement and Rules of Conduct. These rules help protect the entire Guild Wars community from abuse by providing a set of guidelines for fair play that allow all players to enjoy the game. Real-money trading activities negatively impact the fun of many players.