I said no to blurbing a book yesterday. The publisher asked for a review, by July, and it seemed more like asking for a blurb than a "review," which would be typically solicited by a third party, not publisher or author. The publisher referred to the book as an "anthology"; it is not, it is a unified collection by a single author. The translation did not please me, either. It is true that in Spanish the word antología is used for what we would call a "selected poems" in English, but this was not a selected poems and we don't use the word anthology like that in English.
I've decided not to blurb books that I do not love, any more, or that are only marginally good. I always feel that I am being nice rather than sincere, and the praise often sounds lukewarm anyway. I'm surprised people even use blurbs by me that say that a book is kinda ok. I also think I won't review books any more. I often make exceptions if I want the book or would read it anyway.