Shadchanus doesn’t quite work that way. They HAVE to pay up!
Why? I believe even Bais Din would not say so.
DY: All professionals that I have dealt with have told me what they will charge up front. If they can’t give me a number but expect to be paid, then I will not use them (I tried it once and got burned, and decided it was not worth fighting the extreme overcharge).
All in all Of Course is “right”, but I think “on the ball” has the best attitude here.