Ghost writing a book, a speech, or even a magazine article requires a different understanding between writer and recipient.  Learning the voice of the recipient is essential in order for the writing to be believable.  That takes time and understanding.  But the other essential element is for the writer to understand that, once purchased, the writer no longer has any claim to the written material.  A true ghost writer remains off-stage, and never reveals his or her involvement in any written piece.  I am such a ghost writer.  It becomes your work, not mine.