I feel like you guys think I asked them to rate themselves 1-5 on the subject. I did not, I got their resume, where they themselves rated them on the subject. With my question I was just checking whether that self-assessment was correct. I don't see how that is a bad question... Should I just believe their resume? Should I give them some programming assignments? Should I ask them to write a complex algo on a white board? I feel like just asking is a good way, personally, but maybe I'm wrong.