I will read the worst reviews. I want to know the rational people used to not like a book. BTW, I am assuming we are talking recreational reading here.
Cover art has little effect on me as I don't buy other than ebooks anymore. Plus gone are the days of the really great covers of the 40s-70s.
I I don't really read samples though. But reviews by real readers matter to me and I also often find the NYT Book Reviews worthwhile as well. A single review will not induced me to buy or pass a book by, but a selection of reviews will help. But as I mentioned, I don't care about the positive reviews, especially with authors I am familiar with, it's the negative/lower end reviews I do read. Plus the negative reviews are often the funniest stuff!
As for the poll I did not answer as, individually, none of the options fit my decision making process. I use a combination of the options along side intangibles which are difficult to express.
Nice thread...interesting to read the process of others. Hope you are able to glean some useful info from the comments.