Well, as I said in the other thread, I do judge books by their cover. It's such a broad topic, though, it's hard for me to generalize. It's definitely possible for a cover to turn me off, if it looks cheap or childish (for a non-child book), or seems at odds with the plot summary.
I see a lot of this when I go looking for free Kindle books on Amazon, which often come from less-established authors without a big publishing house behind them. It's a crucial form of advertising, because we live in an age when there are so many books to choose from, and it's so easy for someone to make a work available with little-to-no vetting by experts. On Amazon the cover picture is pretty small, like a postage stamp, so if something looks bad even at that distance, I'm not interested.