The problem
A visitor lands on your site and spends a few seconds deciding whether you are real. Most of that judgement happens before they read a word of your copy, and almost none of it is about what you claim.
Reviews are the strongest single signal, and they are not the only one. A page with excellent reviews and no address, no photographs of anyone, and a contact form that goes nowhere still fails the test.
What actually works
What actually makes a site look credible, roughly in order of weight: reviews from a platform you do not control, a real address and phone number, photographs of actual people and premises, specific rather than generic copy, a working contact route, and a clean checkout or enquiry flow.
Reviews earn their place at the top because they are the only item a visitor knows you could not have written.