To publish a book that contains the words of philosophers without giving references and source material is ludicrous. Don't just tell me that someone said something, give me give me chapter and verse. In what book did they write it? Which newspaper quoted it? In which magazine was the interview found? When and where did they deliver the speech? There is an endless supply of books and internet sites that quote famous people incorrectly. The common element in all of them is that they don't give the original sources. Every quotation in this book may be factual, but without citing the original sources, there is no way to know short of doing the research the author should have done with each and every entry.
Unsourced quotes are just gossip.