Abe: Look at the Rama. (of course if the custom is to return the shadchanus money then that is the halacha. I was simply pointing out what the halahca is if there is no clear cut cusom.).
The point i was making is that halacha views the shadchans role to bring the couple to engagement/chuppah. It is not the shadchans job to ensure that they have a happy marriage. For some reason there are posters in the cr who seem to think the shadchan is responsible for all lack of middos chinuch parnasah etc…
It goes without saying that a shadchan who deliberatley misleads either party is obviously a mazik.