It was nice working with you!
I want you to be proud of what we create together. Please take a few moments to let me know about your experience working with me, the whole process, and of course the finished product.
If you have any questions or concerns I will absolutely get back to you and help resolve them. I may use your response as a testimonial. 
Got it! Thanks for the feedback. If you had anything that needs a response I'll be getting back to you shortly.We should work together again some time!