PBA- I have to say I disagree with you on this one. First of all, if a shadchan invests time and energy into a shidduch and you break it off, its only fair to tell him why you broke it off. Imho its a lack of hakaras hatov to just say no without telling him why.
Secondly, it will usually work to your advantage if the shadchan knows what was not to your liking so he can better match you up next time.
Thirdly, on behalf of all those that talk about the shidduch crisis all day, if a shadchan tries and tries and doesnt know why his ideas arent working out, he will give up.