Re: Leaving feedback on Amazon...
I have exactly that problem when I'm scoring books in my own database. I read a cracking space opera that I thoroughly enjoy and give it a five. Then I stop and think is it really as good as some of the great classics I've read, for example something like John Wynham) and of course the answer is no, although they might both be SF they are, in fact, such different types of books that it's not reasonable to make that comparison. Now that is fine for my own database I can mentally make the necessary qualification, but it's much harder with a book I've not read being rated by someone I don't know.
I take those star rating with a very large pinch of salt and look instead for the review that can express the qualities of the book with considered words (rather rare I find!).