Heck, it's like going to the movies... Do you know what you are going to get? The correct answer here is 'a movie', not 'a 2 hour+ long movie' or 'a movie that I will really like'.
I worked at a movie theater. You'd be surprised how many people ask for their money back if they thought the movie was bad, sometimes after watching all the way to credits. I agree with your overall point that this shouldn't be the case, but we live in an entitlist society anymore.