In what way is Montresor an unreliable narrator? How does the use of an unreliable narrator influence readers' views of Montresor's actions?

Montresor is capable of plastering Fortunato into a vault, but if he’s lying we still can't trust him because he isn't very trustworthy, reliable. It can influence the readers in many ways, for example they probably don't trust others as much as they did before.