Submission guidelines at the Dystel & Goderich website (original emphasis): "[Y]ou should describe in two or three sentences—no more—what the book will be about. This is followed by another brief paragraph on why it is being written and then another on why you are qualified to write it....Finally, there should be a more formal narrative Bio of the author."
I can speak of what she was like to work with and how she generated material. In my dealings with Dystel, I found her exceptionally thorough and very professional. She had a template she wanted non-fiction writers to follow, and my writing partner and I followed her template closely. She was rather fastidious, going so far as to mail a personal "Season's Greetings" card in December.
All material she used in our proposals came directly from me and my writing partner. She edited our rough-draft proposals and gave us feedback, but the final versions were all ours. Our final versions, bio included, were then simply photo-copied, by us, and distributed to potential publishers. This was back in the pre-Google days, recall.
Full story: http://www.breitbart.com/Big-Government/2012/05/18/dystel-biography