Apart from reviews and researching the author and his/her previous works, one can always take a look at the bibliography, footnotes and sources. If there's none or very little, and mostly based on secondary sources, one is advised to exercise caution if the subject matter is somewhat controversial. Not that knowledge of primary sources means that the author is impartial (google "David Irving"), but original research is more likely to yield new knowledge and/or more accurate interpretations of events.

Varangian wrote:Apart from reviews and researching the author and his/her previous works, one can always take a look at the bibliography, footnotes and sources. If there's none or very little, and mostly based on secondary sources, one is advised to exercise caution if the subject matter is somewhat controversial. Not that knowledge of primary sources means that the author is impartial (google "David Irving"), but original research is more likely to yield new knowledge and/or more accurate interpretations of events.