The most obvious and credible source you can use to convince prospects about the value of your service or products is your existing customers.

Customer success stories are always effective, but some are more powerful than others. Make sure that their story describes the problem that the customer is solving with your solution. Give lots of detail. Make the customer, rather than your product or service, the focus of the story. One of the easiest ways of collecting testimonials is by using LinkedIn as this has a specific function to allow you to do this.