When a client is nervous at a meeting: What should the salesperson do in such a situation?

When we talk about business meetings, we usually assume it's the salesperson who's nervous and who should look confident. However, sometimes it happens that it's actually the client who's nervous. There are numerous reasons why. It can simply be a young person who is not experienced in business negotiation, or it might be a new employee of the company who needs to handle the situation well. It might just simply be someone who is nervous by nature. How should you handle a person like this at a meeting?