[@Oliver]
Callie doesn't sell her charms to known supernatural beings, and it would be common knowledge how to use them. They are a small, round redwood disk, and are worn like a necklace, as long as they are pressing against skin, they work-so the moment they are in someones hands, they will be working. They are basically potions infused into the disk, and...once invoked they just work lol. Typically worn around the neck