I have seen this suggestion but I can't find where it was.
Make a machine like a vending machine only have it buy a specified item. User will place the item in and get the specified amount of cubits from it. This would speed up the buying and eliminate the need for signs to tell players our buying list and the need to find the buyer to do the transaction.
I also think this would improve the economy as the player in need of cubits would get cubits faster than trying to find the owner of the realm then setting up a time and place to sell their items. There would also be less confusion than trying to buy a lot of the specified items in a cash register where mistakes and scamming can happen. A set price for a set item is so sure & safe imo.