How to sell your work?

When we published "Designing Movies: Portrait of a Hollywood Artist,"

our agent sent in three chapters which were written by my late husband, my co author wrote a sample chapter in the third person based on interviews we had done with pretty much the entire cast of Catch 22. 

We sent these out to 5 publishers.  Greenwood Praeger was the only publisher to respond, we accepted their offer, got an advance and spent the next two years interviewing people and finishing the book. They published us in 2006. 

So each publisher is different in what they want. This one required sample chapters.