Just to be clear, I'm not talking about scholarly work of the sort that might be published by a university press. I'm talking about work by people like Goodwin, McCullough, or Larson. These kinds of books usually don't have in text citations. References will come at the end of the book, usually marked by a book page and phrase.
I realize once the writer has a contract the publisher will probably specify all this. However, I would like to format my work from the very beginning, e.g., sample chapters for proposal, so that I only need to make minimal formatting changes later.