A testimonial is a recommendation which is written by a happy customer or a celebrity confirming the quality, satisfaction and/or value of a service or product. In marketing, testimonials are very decisive in the customer's perspective.
Using testimonials is a must and being applied by many companies worldwide, however, the marketing department of the company must be careful working with celebrities. Their lifestyle may influence people negatively. In addition, celebrities every now and then facing scandals in their lifetime even if its made up by the press.
Testimonials are effective because potential customers tend to believe feedbacks and suggestions that come from outside of the company.
They think that they can trust testimonials unless they look fake and unnatural.
The goal of a testimonial is to show the potential customer that other customers were happy using your service or product. More the satisfied customers are reliable, more the testimonial is trustworthy.