Stack confirmation suggestion
Alot of players complain when they accidentally buy a stack of an item and loose all their money. Can you make it so players need to confirm if they want to buy 1 stack (shift right click). This would prevent players from accidentally buying a stack of items. A gui would be best suited for this. The title would be something like "Are you sure u want to buy?" or something along those lines.
I can see how that could lead to issues, the feature is from a time before Minecraft repurposed sneaking+clicking to not execute the block's but the item's action :S
A confirmation GUI could lead to people complaining about having to do another different action, maybe something like having to click another time to confirm could work better.
For now I suggest to just disable the stacking feature if it's that big of an issue.
Maybe a way to choose how many items shift buys. Instead of default 64 i could change it to 8 so its not a major issue to buy 8 of the item. Whereas sell could stay 64.