Q's about reviews on Amazon

Has anyone had difficulty with writing a review, and then it doesn't post? A reader emailed me, has tried twice to write a review on one of my books, and it will not post.
I, too, tried four times last year to post a review for a fun read for a UNC professor of creative writing, and it never posted. Any explanation will be useful. In all examples, the reviewer was definitely logged in on their account. Does Amazon not post all reviews? Also, a family member purchased 20 of one of my books to give to her circle of friends, and it never showed up on my stats.