Having an auction house would save time. Having an auction house would allow you full access to items being for sale; retainers "crash" and you are not offered the same access to items. Really, I can't think of any reason why it's better to waste time walking to retainers when you could just make a straight purchase. I don't want to browse other people's stuff. Retainers would be good for bazaaring items that need to be repaired or for storage. Retainers may be useful for rare/ex items you can't put on the Auction House. An auction house just makes sense for players that want to make a purchase and be on their way. Please install an Auction House.