I'm trying to figure out what somebody is called who gives you (or someone else) a tip on real estate brokerage.
I've Googled (and Bing'ed ;)) along and found translations like "whistleblower" or "tipster"... Where I think "whistleblower" is mainly used in negative terms (someone who reports abuses and such) and "tipster" is mainly used in the sports-section.
So, how would I call somebody like this in real estate terms?
Edit as per the request in the comment:
It's seen from the agency perspective, saying "John Doe has given us the hint that Jane Doe would buy this real estate". Then John Doe is the [*] of this agency, so they could sell their real estate to Jane.