I added real testimonials to the end of a salesletter. Most of them briefly described their past, what they did with the course, then their future results i.e. what a good testimonial is.
I tested two versions of them (one variation was shorter with testimonials using ellipses to remove possibly unimportant information) and both generated the same number of sales.
The testimonials were added after the johnson box and p.s. statements to the end of the letter with a call-to-action of buying at the bottom of the testimonials (double your dating style).
The control of no testimonials generated 0.4% more sales (96% significance). However, both testimonial factors lead to 0.5% increase (85% significance though) in click-through to the "order page" which is an upsell.
What's some possible explanations for this? My thoughts are the testimonials do not speak directly enough to the market's problems. I might have to test sprinkling testimonials throughout sections of the letter to back up statements.