Exactly. It would have only been justified if the manufacturer and seller were the same entity. He should have given a honest review based on the product itself

Exactly. It would have only been justified if the manufacturer and seller were the same entity. He should have given a honest review based on the product itself and then it would have been appropriate to point out that some of the reviews might be paid. Or better yet: report the seller to Amazon. But the way he wrote the review makes it sound like he rated the item with 1 star solely based on the malpractice of a seller. Companies like Logitech are usually not involved in shady business like that (they hire professional reviewers through third parties, not entice regular customers with 10 bucks, jk :D).