I would at least go and check out the bird or I couldn't live with my conscience. When I made arrangements to get my Rudy, I drove from Georgia to Arkansas and didn't know if I was even going to bring the bird home. If the bird didn't come home with me, it would have ended up in somebody's barn with a bunch of other birds. That didn't sit well with me. Sometimes people say there is a rehome fee just to see if anyone interested is serious and may not charge at all. I have read about this which makes me very happy. I didn't pay a rehome fee for my little boy but paid in other ways such as gas for 24 hour driving trip, new cage and toys. It was a long drive, but very much worth the trip. If the current owner really wants to get rid of the bird, he may drop the fee.
Birds that are abused will scream but maybe with a little work and new environment, the bad habit of screaming will stop. I also have a macaw who screamed a lot when he was younger. He was not a rescue, but screamed for no reason whatsoever. He doesn't do it any more.