The Auction House is where players can put their items up for auction.
Auction House Locations
Auctioneer is located at 7992,2993 in Sanctum which is the NE portion of the city (just east of the northern corner of the pennant when you look at the Sanctum city map).
Auctioneer is in the south central part of the large open area. Map coordinates 6094, 5252.