This update allows the use of custom items.

Custom Items
To set a custom item (the one in your hand), use the following command:

/shop set <shopId> <slot> <buyprice|-1> <sellprice|-1>

Setting a value to -1 disables the buying/selling feature.

Inventory Permissions

Code (YAML):

shopId:
    rows : 3
    title : "&aMy shop"
    permission : myplugin.somepermission # You can remove this if wanted.