Shopkeepers should charge a very high usage fee for using a charge from a store-owned wand of wishing, though not more than the wand costs by itself.

The usage fee for reading a book in a shop is reduced to 45%, to make it so that unless you have very high Cha, it’s better to pay the usage fee than to buy and resell.

Usage fees can never exceed the original cost of an item, and when you buy the item, any usage fee is removed (it’s only charged if you use the item without buying).

Fountains, sinks, and other dungeon features can generate inside shops. Using them in any way incurs a usage fee. Destroying them incurs a larger charge to be paid immediately, or the shopkeeper will get mad.