Quantity selector would be great in market board trades. It's... strange that you need to sell/buy stackable goods in -exact- quantities over the board. It's tedious and wasteful for the seller, and frustrating to buyer - because seller has to try to guess what exact quantity the buyer will want, and the buyer rarely finds the right quantity at right price. Why can't you just put the amount you want to sell in on single stack (up to 99 of course), and let buyer buy as many as they need like in any -reasonable- regular shop.