One of the most annoying things that can happen is buying a book second hand and then finding out that it is full of underlining and highlighting. This happened with Petersburg, which I read earlier this week. However hard you try inevitably your eye is drawn to those parts of the book and you end up giving them more weight than they perhaps deserve. I was always told that writing in books was a heinous crime and one particular teacher at school said those who did should never be allowed to borrow books from a library. Not sure I would go that far but certainly if you have underlined a book to death you shouldn’t then sell it on.