Even reviews that seem very genuine seem to have an affiliate link(s) very often. I came across a great site the other day, and you can tell the author was very knowledgable on the subject, because the content on the site was very original in thought and well supported with research. However, it was not until the next day I realised many of his links were actually affiliate links (to amazon and three or four other stores), as I thought they were mostly connected to other sections of the site. He has a lot of traffic, big return visitors, tons of genuine comments on many of his articles. You can't tell me he isn't motivated by the affiliate links he will add to the content each time he writes a new piece.