"Dear Mr Simpson,
People are often quicker to complain than give praise, and I thought I would start off by forwarding praise where it is due. We were very impressed with Luke and his colleague from your firm today, who installed a new fire and surround in our living room.
They were polite and very professional in their approach and attention to detail. Thank you once again for a job well done and could you please let them know how pleased we were.
Yours sincerely,
Mr Tasker-Plymouth"