What's a "Book Doctor?"
Book doctor is a term from the publishing business, which I was in before I got into the used book business.
The term means, basically, an emergency editor. A book doctor gets handed bad manuscripts -- ones that the publisher has already paid for -- and has to fix them up in fast time. I was in the business of nonfiction so when one of these messes was handed to me, I would check and fix any misspelled proper names, check and correct any incorrect facts, and so on.
A similar term in showbiz is a script doctor.
Now, if you thought I was someone who fixes old, damaged books, sorry, I'm not. For that you need a bookbinder or a document restorer, not a book doctor.