Hear hear. Personally I won't buy from authors who do that. At least not more than once. David Eddings, for instance. Not a bad writer, and I've read some of his books through libraries or friends, but his habit of finishing a book on a cliff-hanger is just cheap, and I won't support that with my money. Tolkien...OK, I'll give him a pass because he's dead and he did a really nice job, but I still much prefer the Hobbit to the trilogy...
But hey, whatever works for you. I know lots of people who enjoy that sort of thing.
Besides, unless you're one of those fanatical early adopters, or you can't be bothered to do your homework, it's not like anyone can really trick you into buying entertainment without knowing what you're getting these days. Easy enough to find lots of opinions online first.