I can't stress how important this can be to making this a pleasant experience

Make polite contact. I can't stress how important this can be to making this a pleasant avalon aron experience for everyone.

Remember that whether you are a buyer or a seller, the other person may have many items posted, or many bids so be specific when indicating the item you are talking about. Also, remember that people are in the game to PLAY.

When your initial greeting is responded to, ask them if it's a good time to trade. If they are in the middle of a mission, or other game activity, be polite, and give them the chance to finish, simply ask them to contact you when they are done.

Also, if your initial contact is NOT responded to, wait for a period of time, (I recommend a minimum of 15 minutes), then repeat your greeting.

People will often either step away from their computer, or be in the process of mapping from one area to another and will miss messages. If in game contact fails to get a response, send the user a PM through the auction system, and/or email, asking for a time frame that is convenient for them to complete the transaction.

Always remember that Guild Wars is a global community and your trading partner may live on the opposite side of the planet, making time zones problematic.