I'm not necessarily going to have the same taste level or opinion as someone else when it comes to a book that is good or bad. However, if the book suggests doing something dangerous and/or contains errors that could cause someone to learn incorrectly, they end up in my recycling bin instead of my donation box. For example, I recycle technical manuals (specifically computer manuals) where the quizzes are graded incorrectly, or if they provide references that are obsolete, like if the book recommends using obsolete html code.