It was a pleasure working with you.
Thank you so much for putting your trust in us for the realization of your hopes and dreams*.
*(or at least your projects)
The only thing that could make me even more grateful for your patronage is a few more minutes of your time. I am collecting testimonials and reviews from previous clients to help boost our future ambitions. Thank you!
Sincerely, thank you for working with us. I hope to work with you again in the future!