You can cast an entire advertisement in the form of a testimonial, as in this one for Austin cars. When the headmaster of Groton discovered that the ‘anonymous diplomat’ was the author of this book, I found it expedient to send my son to another school. Testimonials from celebrities get high recall scores, but I have stopped using them because readers remember the celebrity and forget the product. What’s more, they assume that the celebrity has been bought, which is usually the case. On the other hand, testimonials from experts can be persuasive – like having an ex-burglar testify that he had never been able to crack a Chubb safe.