Witches can trade in my world because they are set to exist like NPCs (non-player characters), like villagers, shepherds, blacksmiths and so on. So players can trade with witches in exchange for potions, tears of evil spirits, forks, apples and other items provided by witches.

After the player finds the witch, he can start trading with the witch in the witch house, and he can get a lot of materials by trading with the witch.