Thought I'd start off with some of the simple but still my personal favorites.
Could range from female teacher deciding to take advantage of a failing student but ends up getting the tables turned on her. Or, student blackmailing her.
Could be a male teacher giving some extra credit to his straight A female student. Or a bit of degradation done to the cheerleader.
The Mail Order Bride
She arrives at the house of a well off older gentleman thinking that her situation has changed for the better. But instead he is harsh and mean. Dresses her up like a doll. Controls what and when she eats. Teaches her English with a heavy hand.