Near the decision point
A testimonial 200px above the CTA outperforms one in a dedicated testimonials section. Proof works when the prospect is deciding.
Specific > generic
A specific quote with a name, company, and role outperforms 'average 4.7/5 stars'. Individuality lends credibility.
Avoid the wall of logos
One prominent logo strip is great. Three competing logo strips on one page create noise. Logos are social proof; more isn't better.