I published an ebook about six months ago, which has received quite a few downloads since then. A few people who read my book are wondering how they can submit reviews.
You never said where the books were purchased. If it's here they can sign in and add the review. If Amazon they can sign in to their account there and add a review.
Lulu account holders can submit reviews on the book's page on our bookstore. They do have to be logged in to their account to place the review.