> developer was good when he's working alone on a project with no one to talk to

or he/she could have faked the resume, or dressed it in a good way. I find that excellent programmers tend to be good communicators, because good, clean programming is about communicating with future programmers (which could be yourself in 5 yrs time). Having clarity in thought and being able to express ideas to other people is so crucial that i would rank that above experience with a certain stack/tech.