Research costs money. When it comes to writing books, that money often comes from the advance paid by a publisher based on what the author claims the book will say. The problem is that until the research is done, there is no way of guaranteeing that there actually is the evidence to back up the claims that the author used to sell the book idea to the publisher. What if all that time tracking down participants in historic events and poring over paperwork in the National Archives fails to come up with the promised goods? Quite often the author cannot afford to repay the publisher's advance, which was not only spent on the research but also on day-to-day living costs. All too many writers might be tempted to package the thin evidence to make it look more substantial than it is and hope that enough readers don't notice the con and that his or her reputation is not too seriously damaged. I suspect that too many reviewers, often authors themselves, cut the errant writer too much slack when it comes to exposing the research flaws and inadequacies of books to potential readers.