Dear Patrick,
Just to thank you for the wonderful work you did on both my oven and the hob ... ten years of grime and muck have magically disappeared and I'm left with a thing of sparkling beauty. I say magically, but of course you had to put in more time than usual due to the shameful state of the oven.
Again, thank you so much for the work and I promise to be kinder to my oven in future. Hope to see you in a year.
I should add that I wouldn't hesitate to recommend you and have already told a couple of people about your service.