Letter of recommendation

Recommendation of a product,service
Use the T.E.A.S.E formula to write a great testimonial. T.E.A.S.E ing will make sure that the people who read the testimonial have a higher probabibility of buying or recommending a service, person or product.
Tactful
Emphasize
Authentic
Short
Engaging

Start with:
“Dear Prospective Buyer/Seller”,
“To Whom it May Concern”
“Dear Mr/Mrs”
Great phrases to endorse the product/service:
“We have found their materials and labor services to be exceptional”
“We look forward to and anticipate keeping the same relationship with”
“I look forward to working with you again in the future.”
“Their ability to work quickly has consistentently proven to be a great value to our clients.”
“As busy as they are, they make me feel like I am their most important priority. And finally, they are not only professional they are a pleasure to work with.”
End up with:
“Please feel free to contact me should you have any questions regarding the above”
“Please don't hesitate to have them contact me for your glowing review.”

Recommendation of an employee
Begin the letters with a sample statement of intent or purpose you are recommending someone, why you are sending the recommendation to them, and the name of the person you are recommending.
Second include a statement explaining your relationship with the person you are recommending in your sample letters. Discuss any professional relationship first, then personal, followed by length and extent of relationship.
Third offer factual information in your letters supporting your recommending someone including a sample of their performance, professional attributes, and personal character traits you admire.
Next provide testimonial statements in your recommendation letters indicating sample situations as evidence why you would recommend someone.
Lastly restate your sample endorsement specific to the position you are recommending someone followed by an offer in your letters to contact you for more information needed