Does a book reviewer (whose review will be published) have an ethical responsibility to give a fair and just book review?
Does that responsibility just extend to the author, or to readers of the review as well?
Yes, a reviewer has an ethical responsibility to authors to give a fair and just review, and a similar obligation to the readers as well. The author may have money, a job, happiness, and reputation at stake in the review, and so an unfair and inaccurate review can wrongly harm the author. Readers, however, have an interest in allocating the finite time and other resources of their lives well, and there are opportunity costs to reading one book when others would serve their interests better. So, an unfair and inaccurate review can harm readers, too.