I think the question is already answered in it's asking: [... fail to show them...].
I think it depends on what you are looking for. Sometimes people doesn't seem to be good programmers, but rather need good guidance. Some people have to be free to fully unfold their potential. There is really no black-white answer. In case of the questions of the interviewer: For the generel interview process: Ask open question and let them talk about their passion. ( A person who just thinks about programming will deliver some day). For technical process: Let them talk about bugs or problems they have encountered. If they can't name any you know straight away. :)