I had one where on the first day of the semester, the very first thing the minute the class started, the professor casually said "if you do every homework problem in the book, you'll get an A on the final."

Not everyone was there on time, some students were going to drop & add the class and most people weren't paying attention.

He casually joked for a couple minutes then settled down to get started.

There was never another hint.

When the final came, each question was verbatim from homework problems that were not assigned.