What to do with a nervous client at a meeting?

When we talk about business meetings, we usually assume it is the salesperson who has a reason to be nervous and who should give off a confident appearance. But sometimes it happens that it is the client who is nervous. There are numerous reasons for this.

It might simply be a young person who is not experienced in business negotiations, or a new employee of the company for whom the handling of the situation is crucial. Or it may simply be someone who is nervous by nature.

How should you treat such a person at a meeting?