From a Christian book's perspective, books that are written in a way that the smartest non-christian could have written, are really just not worth any "christian" value. My thought, after reading up on some reviews on a book "Counterfeit Gods" by Tim Keller, strongly recommended by someone to me. On Tim Keller, I think despite his theological skills, he seems to lean towards social gospel while being pulled by reformed doctrines.
Secondly, those who easily give away their copy (usually the only copy they have) of their "highly" recommended book, are obviously either lying about their value for the book or simply too shallow to treasure the content of a book. But perhaps I would pretend they have PERMANENT photographic memory.