How reliable is the narrator of the tale? Is the mariner still under a spell at the end of the poem? are we his auditors, also?

The Mariner is on the creepy side. He hangs out near weddings hoping to trap people into listening to his "trippy" story. If we can accept this old guy isn't drunk or high and we are open to the supernatural, the story works. He has no reason to manipulate us other than to convince us of the sanctity of all life. He wants the audience to cary the message so the same mistakes are not made by others.