I think dueling arenas and auction houses like this would be fairly easy to implement. Thumbs up
One thing, maybe have it where at the Auction House, all the players inside the major city and possible those on the near outskirts can hear the Auctioneer. That way it gives people incentive to use the feature, whereas those players that simply spam "SELLING BLABLABLA, OPEN TRADE, PST!!!!" will only have a remote distance that others would hear them, assuming that there will be no global chat for non-guilded/non-factioned players.
(Guess it depends on how the chat system works -
chat thread)