Never.

It ruins the book.

I know a book will be good if the writing is good. I prefer first person and the font has to be certain way. If I can read it without it burning my eyes and confusing me, I'm a-okay.

Sure, some people read books and rate them.

I read books to learn and get inspiration, I don't really care if they're good or not.

So no, I read the entire book and then the ending makes sense.