For people who write/draw in library books. Especially in pen.
Like the book on Alzheimer's I found. New book, just a year old. Lots of pen underlining. Or how about the math equation books with all the answers filled in?
Or the books on costumes with notes and everything written?
Thankfully I can erase most of it. But the ink stuff won't erase out. And in that case, the book has to go.