If you go to the guild center in any of the capital cities and get a guild charter, you can annoy people with the "request signature" button. If they aren't in a guild, it will close all of the windows they have open--vendor, auction house, etc.
I noticed this when I was doing a long AH post scan and I got a signature request. Fairly limited use case, but it could be used to annoy some AH players on your server if they aren't in a guild.
Did some testing regarding this, and interestingly enough... if you open a trade with somebody who is using the AH, it will return the message "that player is busy" but it will close their bags anyway.
I noticed this when I was doing a long AH post scan and I got a signature request. Fairly limited use case, but it could be used to annoy some AH players on your server if they aren't in a guild.
Did some testing regarding this, and interestingly enough... if you open a trade with somebody who is using the AH, it will return the message "that player is busy" but it will close their bags anyway.