Here is a great template to ask for reviews/testimonials. Do not ask for a review until after the service has been completed.
Dear [Customer Name],
We hope this letter finds you well. We wanted to take a moment to thank you for choosing our services and entrusting us with your [insert service provided] needs. It was a pleasure working with you.
As a valued customer, your satisfaction is our top priority. We strive to provide the best possible service and ensure that your experience with us is a positive one. We are writing to you today to request a small favor - if you have a moment, we would greatly appreciate your feedback in the form of a testimonial.
Your testimonial would help other potential customers learn about our services and the experiences of those who have worked with us in the past. Your words would be invaluable in helping us improve our services and continue to meet the needs of our clients.
If you would be willing to provide us with a testimonial, we would be happy to provide you with some guidelines and suggestions to help you get started. We understand that your time is valuable, so we have made this process as easy and straightforward as possible.
Thank you for considering our request, and thank you again for choosing our services. We look forward to hearing from you soon.