After reading the book, it doesn't feel like an honor anymore, it feels like a trap.
Because you don't like the book.
You don't want to insult the author/friend with an honest "I didn't like it" tag, nor do you want to lie "I loved it!"
Sticky situation, yes, but it doesn't have to be, you're getting yourself worked up for nothing. You don't have to say you loved it, or even liked it. You are not required to mention the love triangle would bore your 90-year-old Puritan grandmother, or the over-description slowed the pace so much a snail was Indy 500 worthy in comparison. Nowhere are there rules for writing blurbs- except one: it has to come from the heart. Seems like a conundrum?
Consider this: "Fashion, witty prose, intrigue, and action- Blonde OPS has it all!" Author/publisher/ friend Shannon Delany wrote this blurb. Does it tell you if she absolutely adored it? No. Couldn't put it down? Nope. Had to create a fan club or she'd die? No way. What Delany does is tell you what the novel has: fashion, witty prose, intrigue, and action (all true). Those key words alone should help the reader decide if they want to read it. Using my own books as illustration (lest there be any misunderstanding about how wonderful everyone else's book is), here is the review for Sirenz Back in Fashion from Booklist: "The experiences of this sartorial odd couple are funny and entertaining... Bennardo and Zaman are bringing the gods into the twenty-first century." What a great review, right?
Well, kind of. Booklist was middle of the road; it liked some aspects, didn't like others. Those ellipses means there are other words in between the quotes. When using a not-starred review, authors, publishers, agents, and publicists put a positive spin on it by kind of hopping over the not-so-nice parts.
That's how you have to think- compartmentalize. List what you liked about the story; it could be that it's sci fi, that it has a dragon, that there is a tender romance. A few choice words are all that is needed. If I was asked to blurb Game of Thrones, which after three years I still haven't finished the first book because it's so dense, here's what I would say: "Rich and vivid description, deadly royal intrigue, and a diverse cast of villainy, Game of Thrones will keep you wondering who's next to die..." All that is true. And really, I constantly wondered who was the next corpse. Nowhere do I say I love it, or that you should spend your money on the books. Readers have to decide that for themselves. Perusing a few pages will tell them if it's something they would like.
So don't fret if someone asks you to do a blurb. You won't commit a mortal sin by helping an author out with a few words, even if you don't like the story. Blurbs are important because it may draw a potential reader in when they glance at the back cover. With so many books out there, decisions have to be made where to spend limited money. Books without a blurb may leave the impression that they aren't 'good' because no one will endorse them. Celebrities and well-known authors have no trouble getting blurbs. For a mid-list or debut author without connections, it's a struggle. I have seven books (soon eight) with my name on them and getting blurbs from the writing community is a nightmare (and I don't know any celebs) because they are afraid to commit.
Blurbs are an important starting point to book success. If you can help bring a reader to a book, it's the author's job to keep them in. Please say yes and gift the author with a few well-chosen words.