You can't buy specific quantities and undercutting sometimes is really "quick". What if the marketboard work as a first-in-first-out system where buyer sees each price bracket and quantity available (not each listing) and then picks how much from given bracket wants to buy? Then the server would pull it from the list.

Some additional anti-cheese/constant undercut rule should be there as well (like you can create a lower price X times a day while updating your price to lowest bracket is without restrictions).

This could improve listing for mass-items as well as items bought in singular quantities.