What's your FPS like?
Having low or erratic FPS can cause the menu buttons to respond poorly.
You can also create macros with MGE to instantly Haggle + or - 10, 100, or 1000
My computer can easily handle MW, so my FPS is pretty high.
I didn't know about the macros, I'll have to try that, thanks!
Edit: Ok, I found out how to make macros, but it says "you need to have bloodmoon installed for this macro to work," even though I have both bloodmoon and tribunal installed. Maybe it's because my character is level 1? I don't know.