"I am writing this in light of the recent sale of my Ferrari 456.
This is, I think, about the fifth transaction that you have handled on my behalf, both purchase and sale.
I am writing simply to say how impressed I am at the courteous, smooth and efficient way in which you have dealt with this last transaction, as with all the others.
It has been a pleasure doing business with you and Rardley and please be assured that I will have no hesitation in returning to you for help with my next Ferrari purchase."