Would it be possible to create a special vendor, perhaps one per account. This vendor would hold items for sale across all shards. Programming wise, items placed on the vendor would be listed on a master list of items for sale. When peeps want to purchase something universally, they would pick the item from the list. The item would appear in a normal trade window, and the transaction would occur as in a normal trade. Since the item is on a vendor and priced, interaction by seller would not be required. Upon submitting the sale amount, the buyer could finalize the sale. Perhaps programming wise, the item would have to be transferred to the buyer at morning maintenance, or perhaps it is possible to have the transfer occur immediately. I don't know the mechanics required. The key to a system like this would be the sort feature on the list. You could, for example, search for a legendary scroll of fencing, see all that are for sale, pick which one you want and complete the sale.