I Disagree. My experience comes from real life Auctions.
People prefer buying in quantities. The game supports per-unit prices by allowing you to define a quantity (even '1'). If I need 8 X, I look for a seller selling 8 at once, not 2 sellers selling 99 at a lower price.
There is no desire to piece-meal a quantity out because instead of someone "needs 50 X for 99gil" it becomes "buy 1 X 50 times where X is 2gil or below"
When there is a fee per unit price, it adds up. It's often better to NPC items that sell below the NPC price than to waste a selling slot with it.
The reverse is also true, I can buy the stack of 99 if I can afford it, use the 8 items I need and then sell the remaining 91 at the price I purchased it at, but I'm doing that at a much greater loss if the next seller decides to undercut that price.
For that reason it's better to buy the quantity you need at once, even if the per unit price of that item is higher.
A smarter MB would have market-maker NPC's that represent the NPC's in the game, and actually adjust the NPC sell-to price based on MB demand. Thus, players who simply try to dump items, would have the items immediately bought by the MM NPC's and sold at the current best price.
In games that support per unit and per lot pricing, or auctions, it's often a super-frustrating experience to have "good deals" disappear within seconds due to people manipulating the game market.
