Ok I have some more info here everyone.
The issues with Charlie started about 2 months ago at 7 months. He has been to the vet, and had his thyroid checked, but the vet doesn't believes for the most part, this is behavioral, not medical. And no in depth testing has been done on this, the vet believes Charlie may be partially blind in one eye (his blue eye). He also appears to have anxiety, but I believe that's more than likely from not having enough exercise and being couped up.
He's not aggressive towards strangers, but he does show different reactions to different people. Sometimes he is excitable/friendly right from the get go, other times (less often), he is wary at first but warms up after a few minutes.
Warnings before bites - I've been told yes, but that they are sometimes subtle. I personally believe the signs were there in bold to someone who knows dog body language, but my friend being unfamiliar/inexperienced with dogs in general, may not have clued in on them.
He has bit my friend 4 times, 3 of those times were single bites due to food aggression (which a trainer had been working with him on), resource guarding
and one time to my friend accidentally kicking him. She went to kick his toy and he charged in to get it as she kicked it. He bit her when she went to "comfort" and give him a treat.
The 4th bite was the bad one. There had just been an argument over Charlie (he was barking in his x-pen and my friends parents had flipped out about it screaming at her to shut him up). She went over and tried to work on some clicker training with him to give him some stimulation hoping it would calm him down and tried to put him into the "relaxed position" her trainer had told her about. Back turned to her, she walked up behind him and he turned and bit. This time he bit twice, not just once. The one bite did draw blood and was quite deep, though she didn't receive stitches for it.
He has only bit my friend, and nipped twice at one of the trainers during a session.
I should also mention that unaware to my friend of the consequences of it, she has pinned him down at least two of the times he bit her. I'm not sure if it was her way/idea of trying to establish dominance or if it was simply all she could think to do after being bit. Maybe to prevent him biting her a second time. Obviously it hasn't helped matters.
Anyway, I don't believe this is rage syndrome or that he's and unstable dog. I think a combination of stress/anxiety, lack of exercise, being couped up and if he "is" partially blind in one eye have turned a would be awesome dog into what he has become. And I don't think it's time to give up on him.