I recently started noticing some sellers including a little brochure/paper along with the product with something like this written: 'Write a review for this pr

I recently started noticing some sellers including a little brochure/paper along with the product with something like this written: 'Write a review for this product, rate 5 stars in all categories, send us an email at <qqq@qqq.com> with the review ID, and receive a free product.'