in the book thief, why was death a reliable narrator?

Check this out,

http://www.gradesaver.com/the-book-thief/q-and-a/what-is-the-impact-of-having-death-narrate-the-story-79173/

Also, Death has no affinity for any "special interests." He notes that a big part of his job is equality, he comes for everybody sooner or later. This sense of universal fairness certainly makes him a reliable narrator.