If you are reading alone you should investigate the sources of the book, read reviews of those sources if they exist, and read reviews of the book. With respect to who is reviewing them and their interests. This is exhausting but worth doing. I did it for one of the books I had to read for school and found out it relied heavily on an explicitly fascist source (Bloodlands iykyk).

However, if you are reading in a group this becomes a lot easier. The investigative task can be split up or designated to one person per book. Whichever way you organize it is fine but the investigation must be done.

This is more difficult with new/obscure books as they won't have many useful reviews or writeups on their sourcing for you to reference which is why I recommend staying away from these for solo reading until you have familiarized yourself with whatever field that book focuses on. Focus on older books with well established and corroborated arguments until that point.

For example, in the case of marxist theory, read the foundational works of Marx, Engels, and Lenin. Mao too imo but this is controversial lol. Once you have familiarized yourself with these works you can branch out into more obscure/specific theory and be able to recognize bullshit and mistakes where they exists.

Edit: If your book does not cite its sources and isn't a well known historical work, don't bother with it.