I love to rehab Quakers who bite. You know why? (I'm going to speak generically here, because I know there are exceptions.) Because they're really lovey birds underneath, and they catch on pretty quick and respond well if you remember some things:

Don't get angry.

Don't punish.

DON'T take it personally!!!!!!

Assume the bird is either

1. frightened

2. acting instinctively

3. confused

4. stressed

5. doesn't know what else to do.

(None of which means the bird loves you less.)

Now, when I say "don't punish" I mean don't try to get retribution for being bitten. A "time out" once in a while, administered with the idea of "let's calm down" and not "you bad bird", works well. Sometimes the bird bites, the owner gets upset and punishes, the bird gets stressed, the bird bites harder, the owner gets more upset and punishes the bird, the bird gets MORE stressed....well, there really isn't any way out of this vicious cycle unless the owner changes his/her behaviour. Definition of "pet owner": the smarter one who can can get his pet to do what he wants by sheer superior brain power, NOT by physical dominance. (My other motto: "If you can't outsmart 'em, you don't qualify!") 

What do you do if your baby bites you?

Stay cool! Then show him you're the boss and reassure him and calm down the "poor baby". (See, it's all in the attitude you take!)

  If one of my birds bites hard (it happens once in a while), whether I'm holding him at the time or he's in his cage being "Xena, Cage Warrior", I grab (gently but firmly) his beak between my thumb and forefinger and rub it, and speak soothingly to him. If you're holding his beak he can't bite, it shows him you're dominant, and it feels good to him to have his beak rubbed. It calms him down too. It gets him out of whatever hormonal "zone" he might be in. Also, if you're holding his beak, you can sneak a smooch on the forehead pretty easily.

If he's in the cage, I'll bring him out and hold him. (Here I am being dominant!) Once I'm holding him, I hug him up real close and give him kisses and tell him to be a good boy. You can see the look in his eyes: "Uh oh, it wasn't supposed to go this way! What the heck?"

While hugging him (aka, in control of him) I'll say something like:
"What are you doing, baby? Are you being a little Teenage Mutant Ninja Turtle? What's the matter, sweetie? If you don't watch out, I'll give you kisses....! Are you being a good boy? Are you gonna be a good boy? OK? Good boy?", etc. By this time the bird is acting sweet and lovey, and probably WANTS DOWN!

While this may sound like the bird is being rewarded for biting, he's not. He's certainly not getting the effect he wanted from biting! Just the opposite.

After a few times of doing this, all it takes is a stern "UH UH UH UH UH" from you to "remind" him not to bite! Or else kisses!

My Baby doesn't mind other birds, except for my Kiwi. That's because Kiwi chases her around going "Kiss kiss kiss kiss" and making smooching sounds! (I guess you could say she's a stalker!)

So that's what I started doing (kissing, not stalking). It works!