Vouching is not a reliable system. Just because a person vouch for another, does that means that person is innocent. The voucher could be a baddie, or tricked, or bewitched, or charmed, or whatever.
Well, I don't know if this is considered vouching, but I randomly linked up with Crestham yesterday, and I didn't receive any damage. Yup, so I don't think he's a Guardian.