I recently took a class where the Professor created multiple online study guides, on popular student sites, which intentionally contained the wrong answers. He did this because his exams were based heavily on the end of chapter questions in the book. Also, the Professor told us at the start of class using Google to help answer the questions would be useless because all the top results regarding these chapter questions were his wrongly answered guides.
Was this ethical of the Professor to do? The book used in the class contained no answer (or partial answer) keys and no additional student material was provided for the book. I understand he did this in order to force students to read the book and keep them from simply Googling all the answers at the end of the chapter. However, this removed a way for students to verify their answers were correct.
Edit: In response to some of the comments, he was not bluffing. During the course I was unable to answer one of the questions (it turned out to be a misprint in the book) and tried using online resources. The wrong guides were easy to spot, because half the chapter questions involved determining which SQL statements were valid. Some of the guides were simply answered as A, B, C, D, A, B in order down the list. Other were just flat out wrong. Also, as far as the exams went, I shouldn't say they were heavily based on the book. The Professor literally copy and pasted the questions from his instructors manual and didn't bother changing any wording or the answer order.