We didn’t give any shadchanus gelt to anyone when I became engaged.
Hmm… I wonder why not? 😉
On the occasions that I arranged shiduchim, I did not want to accept any shadchanus (but did accept a small gift when the couples insisted).
If the shadchan intended to do it pro bono, there is no obligation.
From this week’s Business Halacha newsletter: http://www.businesshalacha.com/sites/default/files/web-file-manager/files/email-files/Business-Weekly-5771-Masei.pdf
By Rabbi Meir Orlian
Halacha Writer for the Business Halacha Institute