Complex sentence: Some claim that the book is genuine and has only been called a hoax in order to discredit it, and they cite statements made by Harvard professor John Kenneth Galbraith in support of their claims.
Split into simpler sentences: Some claim that the book is genuine and has only been called a hoax in order to discredit it. Some who state that the book is authentic cite statements made by Harvard professor John Kenneth Galbraith in support of their claims.