From Yoast: Testimonials are powerful in creating trust, and not just for online shops. The same actually goes for sales. Research has found that positive reviews can significantly increase sales. In fact, testimonials have been found to be a more important cue for judging the trustworthiness of an online store than the actual overall reputation of that store. But obviously you can’t just slap on some glorifying texts on your site. Your testimonials will have to earn the trust they’ll evoke in your site’s visitors.