If someone tells you that you're not a professional person; how do you respond?

It depends on the situation. It can be a bit of black and white thinking to say you are not a professional person to turn down the validity/helpfulness of what you are bringing. So you could say that you're still valid even if you're not professional. Perhaps using some information would help back you up. Or you could provide your education background. Really, this question is too out of context to answer helpfully at all. if someone is trying to bring you down by reminding you you're not professional, hold your head high. We're all equal.