The hit boxes for the the plus and minus on the quantity select for vendors is really small, especially for the the in-stock item purchase interface. It can sometimes be hard to land on exactly where to click in order to increase the quantity since the cursor is still kind of floaty even on the highest sensitivity. The quantity + and - also have slow response time, you kind of have to pause in between each click to increase the quantity instead of just click mashing it because they will often not register that way. This is problematic since there is no way to input large numbers quickly. On keyboard control it lets you highlight the number as if you could input a number with the keyboard but I've never actually gotten the keystroke to input into that textbox. There is also no "increase by 10" what have you, each click of the plus button only increases by a quantity of one. This makes buying or ordering a large quantity of items incredibly time consuming. Maybe like clicking and holding the plus will make it rise at a rapid rate (wait, does it already do that? I haven't checked, I'm sorry if it is) or increase by 5 twice per second or something. That or just letting you arrow key up or down the quantity.