Often there are a number of qualified candidates interviewing for most good jobs. The person they hire will be the person they feel will most be able to work well with the team. Look for shared experiences, common backgrounds or working relationships. Look for ways to improve chemistry. People are more sold by conviction than by persuasion.
Quiet enthusiasm radiates eagerness to become part of the team.
The fine line between enthusiasm and desperation is of interest. People want to know that if they make you a fair and competitive offer that you will accept it. Know your field of expertise, but think people. Often you may meet a number of people, all of whom have different agendas. The CFO may want to talk money.