“That obviously would depend on what they would pasken is the market rate for the community involved.”
So, it does not depend on the shadchans personal feelings either now, does it. Why do you malign someone who gives an amount less than what you believe is THE proper amount.
“The definition of community is also something needing psak.”
As would an “inter community” shidduch.
“L’maaseh, it rarely, if ever, ends up in beis din, but someone needs to consult with a posek before unilaterally deciding what or how much to give, because it’s a halachic issue and not dependent on personal whim.”
One must also consult with a halachic authority before unilaterally deciding to malign a whole bunch of people because their personal whim calls for $2500 and they only got $750 or a candy dish.
My final thought on the matter is. If the halacha states that in absence of a pre arranged agreement or a pre determined market rate set by beis din (or the market), then the shadchan is not the one who determines the market rate, the market does, and that includes those on the receiving end of the service as well.