For me, blurbs are hugely important to successfully generating a sale/download. Most of the books I don't download (even if the book is free) are due to the content of the blurb. The reasons vary and I have certain sentences and key words that are my red flags.
For example, a book that uses a variation on "x is/was a typical teenage boy/girl". Nearly every time I read that sentence or something similar, I move on. I also tend to dodge anything that has "legal thriller" or "medical thriller" in the blurb mainly because I'm usually just not that interested in either of those areas. And I'm very unlikely to try anything that has a typo or grammar error in the blurb, the darkest of omens.
Tonight I encountered one that needs to be added to my list of red flags:
Each book is twice as long as a standard novel, so you are getting excellent value along with a great story.
So, given that we've discussed before how difficult it is to wade through the Amazon/B&N/<insert retailer here> slush pile, I thought it might be interesting to share our red flags. What will immediately be a swing and a miss for you if it's present in a book's description/blurb?