The Mayor usually wants the Village team to win, and should answer questions in a manner that leads them to the correct answer. Unless the Mayor is a Werewolf, they should be answering the questions with the goal of giving players more information that will help them figure out the magic word.
A good example of an answer that is technically a lie (but a valid response from the Mayor) is the question "Is it an animal?" when the answer is a human. Even though humans are animals and the truly correct answer is "Yes", the Mayor (an innocent Villager) knows that would be misleading to the Villager team and should answer "No".
However, a Werewolf Mayor would be able to answer "Yes" to that (because they're allowed to mislead and lie to players), and then defend themselves on the basis of it being technically correct, even though it would lead the guesses down the wrong path.