Mackey is a shop owner who knew Bobby Singer. Bobby had Mackey's card in his journal.
Mackey is the owner of a Taxidermy Shop and had met Bobby on a job somewhere. Mackey got word of the healer Emmanuel, so he called Emmanuel's wife Daphne. He tells her he has gone blind (was only in one eye) and Daphne told him that Emmanuel will come see him. So Mackey set the place up with traps and tests to see if Emmanuel was the real deal. Emmanuel showed by and passed the tests and healed Mackey's eye.
Sometime later, he gets a call from Bobby's friend Dean Winchester, who called asking for any knowledge of healers. Mackey calls Dean back and tells him his story. Mackey tells Dean that Emmanuel is the real deal.