Difficult client?

We all have heard expressions like a difficult client, tough client etc. What does the term actually mean? I see lot of discussion going on around this. Here is my understanding of the same:

Any client is one who is very demanding in terms of quality of work and very stringent on the cost part and very rigid on the deadlines and who is not willing to give any leeway on any matter can be termed as a difficult client. It will be difficult to keep such client happy. Typically, such client may not be willing consider factual evidence and keep unreasonable expectation from the vendor. Normally, the client will raise a big hue and cry for something that goes wrong in the project. A demanding client asks for good quality at his own price while sticking to pre-defined schedule. When a demanding client is not willing to listen or negotiate, he becomes a difficult client.

The way to deal with such client is to set proper expectation with them. More than technical skills, it is the people skills which help us handle difficult clients.