When I choose a book from Amazon or some other bookseller, I try to see if the author has any affiliation or support from one side of the issue or the other. For example, an environmental book authored by a member of a specific environmental group likely has a bias against big business. An author that works for or has backing from oil companies or other business likely has the opposite bias.
I may still buy the book, but I realize that I am likely getting a mostly one sided argument. Some subjects are hard to find authors that aren't biased one way or the other. Even books by professors from universities have funding from environmental groups and big business. You can't discount this when reading the book.
If you are looking for a book about a certain subject, I suggest buying more than one. A well informed decision can only be made if you are aware of all the arguments and you're not going to get that from someone who has an obvious connection to one side or the other. If you are lucky to find someone that puts out both sides of an issue, make sure to recommend it to friends on both sides of the fence.