I have a friend who used to copy edit books to supplement his income from his day job- a copy editor is basically the person who gets the text from an author and goes through to make sure that the spelling, punctuation and so on are OK before it goes to press. Because he was working on Doctor Who novels, he was extra careful with them, but I would expect that from a publisher's point of view, a TV tie-in novel is low prestige and will be farmed out to somebody cheap and/or inexperienced. My friend copy edited several books before he was actually sent on a course to learn how to do it properly, so the person who was given the Buffy novels may not even have had much training!
When I finished my degree course, I gave away a lot of the books I'd studied because they had so many notes in them that they were practically unreadable- I used to underline things as I went and then put slips of paper in to mark the places that were important if I came to write an essay on the book. Of course now I don't buy physical books any more, so it's largely irrelevant, but I did report one book I took back to the library a few months ago where somebody had made pencil notes under the photos.
When I finished my degree course, I gave away a lot of the books I'd studied because they had so many notes in them that they were practically unreadable- I used to underline things as I went and then put slips of paper in to mark the places that were important if I came to write an essay on the book. Of course now I don't buy physical books any more, so it's largely irrelevant, but I did report one book I took back to the library a few months ago where somebody had made pencil notes under the photos.