Let's start off by using our imagination. Let's imagine you're looking to get a brand new bathroom fitted this autumn, to prepare you for the cold winter nights.
You're looking online for the best local plumber in your area, and you notice that the prices are pretty much the same across the board. You whittle it down to just two plumbers, lets call them Bob and Jim.
Bob and Jim's website's are pretty similar; they've both got established qualifications, they both have been plumbing for over 10 years, and they both claim to provide the most excellent service in your area.
The only difference is, Bob's website features testimonials from real people, talking about how great he is. Instantly, this makes you trust Bob that little bit more than Jim.