In different fields, renowned academics are sometimes honoured with a Festschrift on the occasion of their birthday or in memory of their life. (The Festschrift contains articles by scholars close to them who typically engage with a topic the honoured academic is interested in.)
I could imagine that if someone were to write a review of such a book as a whole, she wouldn't want to be overly critical because it's not nice for the editors and the honoured academic (if still alive). Of course a bad review is never "nice", but since a Festschrift is a present one may want to be more careful.
Then, can we trust book reviews of Festschriften? Is the difference with a normal book review negligible?