How do you evaluate rationally if someone is a genius?

Question:

How do you evaluate rationally if someone is a genius?

I'm not talking about IQ tests, but common sense ideas that help determine that someone has an extraordinary intelligence.

Best Answer - Chosen by Asker: I think the key is in your question: extraordinary. If someone shows extraordinary knowledge in smth, playing the guitar, invention, in general, extraordinary results of one's activity. That's how we evaluate geniuses.