There's a few fairly basic means to appraise quality/reliability when examining a secondary source to get, at least, a rough estimation of its quality and reliability:

• The qualifications of the author. Are they a professor at a good university? A fiction author? A conspiracy theorist? While it's no guarantee, books written by academics from a relevant field are much more likely to be reliable as works of history. Researching and writing history is a skill that must be learned. Note that there are exceptions: if the author mentions spending a lot of time (by which I mean years) in archives in their introduction, the work is likely to be well-researched.

• Branching from there, the introduction is a great way to evaluate the quality. Does the author discuss the historiography? Do they mention professors at quality institutions and their ideas, and how dense are their (foot)notes? A book without any notes is highly unlikely to be an academic work, and a book with relatively scarce notes is pretty questionable unless it's a lower-division textbook. Does the author lay out a consistent argument and how they intend to support it? Does the introduction, and the writer's argument, make rational sense? Can you easily come up with alternate explanations for the author's argument that they didn't address, and can you think of any place where the evidence fails to, or simply doesn't exist, to support their claims (see books like 1421: The Year China Discovered the World.

• The third way is a bit more oblique and won't work for every book, but is probably the most efficient. Look for academic book reviews of the piece—this will be difficult for many books without Jstor access or something similar—and see what other historians have said about the book. Academic book reviews are rarely more than 750 words, and they're written very accessibly and let you know the reviewer's opinion on the merits and quality of the work (and its argument). Also, note that historians are a very fractious bunch, and a negative review doesn't necessarily that the work has no merit.

• Of course, you can always ask us here—if the book has any merit (or notoriety), odds are that at least one of our flaired users will have read it or have an opinion. The book you mentioned, Why the West Rules--For Now, is a pretty popular and notable work.

Speaking of Why the West Rules, I think it's a good time to deploy these on that book itself; I haven't read it personally, so this should work.

Who wrote it? Ian Morris, a professor at Stanford—obviously a great institution. He's a Classicist, meaning that his actually training is in history before 500 AD, which means that the book, which covers all of human history and even beyond it is out of his (and anyone's) theoretical breadth by far. This makes me somewhat suspicious that the argument can't really treat its subjects with the specificity needed to make them function as proper historical evidence, but he's as qualified as just about anyone to try.

The introduction (available in part on Amazon), for a book not intended solely for academic readers, covers his historical background and defines his ideas and terms capably. It definitely suffers from the incredibly huge scope of the argument, though, since the amount of time he spends explaining the place of his argument in historiography is underwhelmed by his need to tell a very long story.

While I'm not going to open up a question on /r/askhistorians, Morris' argument also sounds somewhat like a rehashing of Jared Diamond's argument that physical geography underlies the high level of "success" for the West, which is not popular among historians—a fact you can find in our FAQ, iirc—and therefore makes me even more skeptical of his argument.

Review-wise, this book is popular enough that it's hard to find reviews that aren't at a major paper. These will still give some idea of what to expect, but are necessarily tinged by the fact that the average reader is more interested in whether or not the book is, well, interesting than in its veracity or trustworthiness.

My general feeling towards Why the West Rules, sight almost-unseen, is that there's no way Morris can put together a cohesive, evidence-based argument on this scale in a single (now two, apparently) book. I have an nine hundred page book on the Thirty Years' War in front of me, one that I know necessarily leaves parts of the story out; the sheer audacity of claiming to explain all history in a shorter work is incredible, frankly. If the work was more obvious a synthesis of previous scholarly work, drawing upon a forest of secondary sources to produce a magisterial narrative, I might be less skeptical.

Currently, unless I hear otherwise from a couple trustworthy sources, I'm going to remain skeptical. His argument is far too broad and reaches too simple of a conclusion (as a rule, anything that gives a single cause for anything should be treated with some skepticism; something that gives a single cause for everything needs to be treated with even more).

All that said, I could be completely wrong about Why the West Rules; I'm working primarily on intuition. If you're interested, feel free to ask in here if anyone has read it and has a full scholarly opinion on it.

Post-gold edit: Thank you.

hi! fyi, you can get started with this FAQ section

• Historiography and studying primary sources

The responses thus far are excellent. Rather than repeating them, I will add this:

When reading, ask yourself - is the author grappeling with the facts as they come up, or are they shoehorning the facts to fit into a predetermined conclusion. A lot of bad, politically motivated history fall into this category (like say, "Our Oldest Enemy" about how France and America are implacable foes, written in the throes of 2003's Francophobia). Everyone has an interpretive framework, but honest historians will deal with the implications of events and facts and primary sources first, -then- go to conclusions.

With this question, are you mostly referring to primary sources or secondary sources?