The best way for me to illustrate this point is to show you how top literary agents sell books to publishers... because that's the process you need to model. (literary-agents.com)
Selling scripts to producers is completely different from selling books to publishers; success and contacts in one field doesn't imply success and contacts in the other. (accrispin.blogspot.ru)
Pay a professional, or sell your book to a publisher who employs professional editors. (terribleminds.com)