Why does Apple let people leave reviews for things they never purchased

I want people to be able to read my ibook, and leave comments.

I just tested out this "review method" on an ibook that I've never seen, heard of or purchased.

I tapped the title, and I gave it 5 stars and a review. Even though I never even looked at the content.

Why does Apple allow non-customers to leave reviews. That could kill a persons progress as an artist