How do you know that the candidates has high potentiality of working in the similar field as he/she is getting too much nervous in an interview?

Firstly, the interview is important but not the only messure for hiring consideration. the Interviewer plays important role in making the interview process beneficial such as having the skills in askig the proper questions that helps the applicant discussing about the skills and capablilities he has it that makes him qualified for proposed job. So many prefectly qualified candidates loss the opportunity just because of the poor preparation of the job interviewer.

Secondly, the qualifications, experience & reference letters must be taken in account along with the interview outcome.