I've only been exposed to the use of ghost writers in the context of the music industry and can imagine the same need for such a service within the book publishing. I wonder if ghostwriters write their own public work? And since they have their own individual writing styles, and ghost-write for other authors, if people ever sense the similar writing styles when reading?

It's interesting to me that authors chose to publish through self-representation. In this case it makes sense considering the shortage of literary agents, but this instance reminds me of other creative industries, like the modeling or music industries where models can chose to work unrepresented by an agency, or 'freelance', while some musicians chose not to create with a label and make music independently.