My atoo bites everyone, how can i get him to trust people?

He's around 7yrs old, has a bad past- more then 8 different homes (most due to biting and screaming). Lived in a pet store off and on with improper nutrition, crappy cage, no one-on-one time. I worked at the pet store, it was awful I quit and bought the bird. He hates men, loves to bite. He doesn't bite me, I don't know how I got his trust. I have people give him treats and it helps sometimes. He was a hand fed baby bird who was once nice but not anymore.