Good relations have always been the soul of a successful business. Testimonials are like feedbacks or ratings your clients and customers give about your service and business. They are a written formal expression of trust your existing clients/customers have in you.
It is a very powerful tool that will not only help you form better goodwill in the market but also generates new clients and customers. It lets your potential clients/customers form a perspective about your business before tying hands with you.
If you have bad credit in front of your existing clients, it will reflect in your testimonial and that will not be very much working in your favor. You can create your testimonials by asking your worthy clients. Testimonials are not only given for favorable services you provide to your clients but are also for the positive post business interactions you have with them.
However, not every testimonial you receive will be genuine. Some might be there for their own benefit. You need to filter which one you want to add that justifies your work and relation.