Like Me? Follow Me.
It's such a proven tactic that even the pyramid scheme email spammers use it:
Take the above screenshot - if you got an email from some random guy named Joel telling you to trust him that he was telling the truth about his marketing genius and his surefire way to make money, well, you'd never believe him. But, if his client Phil goes out of his way to tell you about the scheme, explaining that not only has Joel helped him, but he's also helped all these other people - and he gives you their names - doesn't that add a hint of credibility?
Names = real life people = happy customers.
Surely providing real stories about how your products or services have benefitted others, backed up with their thoughts on how great you are in their own words is the best form of marketing there is. There is absolutely no substitute for receiving a recommendation from a satisfied customer.
So, take it from the spammers - testimonials work. They don't send those emails out to you for fun because they like the idea of filling your junk folder. They do it because it makes them money.