Most witches' brews involving such things--teeth, hair or fingernail clippings--don't just need a random bit o' human. Usually that sort of thing is used in either a love spell, or in a spell meant to harm, but the target of the spell would be the donor of the tooth/fingernail/lock of hair. So someone wouldn't want this for witches' brews, unless they were doing something to affect YOU.
Not to say that it wouldn't be a hoot to fleece money from the credulous, but I'm just questioning that there's really a market for this in your target demographic. 😛