We would very much like to take this opportunity of thanking you for a job so very well done. It has been a pleasure for us to have you working here and for all the attention to detail you have shown. Nothing has been too much trouble for you and you have always dealt with our questions or thoughts so thoroughly.
Should you need to reassure a prospective customer that you do exactly what you say you will do and at the agreed price, then we should be more than happy to oblige.
Our very best wishes to you all.