It's lovely that you're conscientious. We know darn well that not all who write blurbs are. However, I don't think you need to worry overmuch. I think most readers, of the type you're likely to attract, are savvy enough to take blurbs at face value. (Judging by some of the comments you've gotten so far, perhaps at considerably less.) I don't think I have ever picked up a book solely because of a blurb. I tend to go by author's track record--did I like someting he or she wrote before--or, when author is new or unknown to me, by reviews. (One bad review won't necessarily put me off, either, though a whole bunch will.)

Heck, sometimes, although I can usually trust them, friends' recommendations don't pan out. Tastes are highly personal and subjective. Friends may jive 99% of the time, but, oh, that 1%. You hate it. She loves it. That's just the way it is and neither of you is necessarily wrong.

(FWIW, I can't stand Diet Dr. Pepper. At least, I assume I can't. Could never drink regular Dr. Pepper so never have tried the diet version.)