Birds bite..that's all there is to that. Birds are not domesticated animals. Part of the reason I love birds is the rawness and naturalness of them. They haven't changed. They're strong. We can't just turn that beauty and natural appeal on and off as we want. That's what gets bird-owners in trouble. They want to have a beautiful and exotic animal but have it do what they want. Birds don't have switches to make their behavior convenient for our exotic ownership wants.
We, as the owner, are in charge of finding what makes them bite. Cecil bit me HARD, still have the scar, when I tried to get him to step up after he was overstimulated from a lot of activity in HIS room. He wasn't angry. I misread him and that's MY fault.
Baby is a rehomed BFA. I've had her for 3 months. I suspect she was abused. Since I put her in our living room a week ago, she has turned into a whole new being. She's still a bit "nippy" at times, but no cage aggression. And she welcomes petting much more now that before as she bends her lil neck and says "aweee". Before she'd only do that rarely and then lunge at me. Having her incorporated into our family "flock" seems to have eased her tension. I know right now that even though she sticks her cute lil foot up to step onto my arm that she'll nail me. She tried and I backed off. She and I are still dating and don't have that trust yet. But that's not her or my fault. She is who she is. I'm working with her on the perch step up.
The good thing is birds can grow to trust you, over time. Trust takes time. BUT...you can't just assume the bird will trust you...even with time. You can do your part to help that effort, but the bird will like who it wants. I've spent a lot of time with Baby and just recently my kids tell me when she hears my diesel truck pulling up the drive she starts screaming LOUD. (maybe I can get them to teach her 'daddy's home' LOL).
It's not about the biting, it's about how you date them into your flock. Make them feel safe and happy...a little at a time.
There are so many variables to this you can't list em: previous hand experience, clothing you are wearing, environment, BREED, sex, mating season. Birds, like kids, would do well to come with a manual. But they don't.
They don't bite for no reason; they are scared, mad, angry, something.
But..should they bite, don't freak, don't scream, don't give any feedback. gently push back (with a hookbill) and unhook your finger/wrist from their grasp as.
I've had people, ignorant people, tell me "thump em on the beak" or "drop em on the floor" if they bite you. People, that's animal cruelty.
<<<NEVER EVER EVER IN ANY WAY PUNISH A BIRD FOR ANYTHING>>>
Woo them into your flock by making em feel safe with you and trust and offer em
FUN and TREATS!
That'll go miles in
preventing biting.
Owning a bird is much like being married. You can't change people to be what YOU want when YOU want em to. (I can say that after 24 years of it.

)
I'm not going to get bitten just to make her do what I want. It's like the 70's song..."I wannnt you to want me".
Mark