One thing that I think might help make more of a competitive marketplace and be an ease to buyers and sellers alike would be an option where a player can sell a stack of items and have players buy a quantity from that stack, without having to buy the stack outright and resell the excess.
So for instance, I have 96 fleece that I'm trying to sell, and usually, if I wanted that stack to sell fast, I'd have to divide it up into groups of 12 or 24 (to keep with woolen yarn's 2-per-1 recipe) at the same selling price. However, this leaves me with the problem that I'm clogging up my retainer's sell screen with 4-8 "stacks" of fleece to sell, and one retainer can only sell upto 20 "stacks" at one given time.
Now, if I were to set my one stack of 96 to allow other players to purchase parts of it, I'd still be paying any tax percentage for the amount sold, but I wouldn't be losing any money than if I sold all at once, and people can get the amount they need at any one time.