“Dear a.e.s.,
I guess it is human nature to complain, but I decided it is equally important to let a vendor who exceed expectations know that as well.  I’ve been counting on a.e.s. to support my business for about three years.
In that time you have helped me with critical placements and done a great job.  One of the most useful aspects of your service is that you not only understood what I wanted but also helped me get a clearer picture of the position, the job description and the ideal candidate.  I believe you have come to understand my needs and corporate culture as well as I do.  This leads to another positive contribution.  Even if I do not have an active search, your staff contacts me when you happen on a candidate who seems like someone I would be interested in.  It has also been very helpful to get your perspective on what the market rate is currently for any position.  That kind of thing is always changing and I can rely on you to be up to date while I concentrate on running my business.
I would have no hesitation giving you the highest recommendation to my friends, clients and family (maybe not to my competitors). In particular, I think your customized help is critical for the small and mid sized firm that can’t afford to hire the wrong person or keep someone on payroll who fails to make a real contribution!
Please accept my thanks, and keep up your exceptional professionalism.”