A good friend and a bad friend are like a perfume-seller and...

A good friend and a bad friend are like a perfume-seller and a blacksmith: The perfume-seller might give you some perfume as a gift, or you might buy some from him, or at least you might smell its fragrance. As for the blacksmith, he might singe your clothes, and at the very least you will breathe in the fumes of the furnace.