"Tipster" in real estate terms

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.

Solution 1:

In a business situation like this a tip is referred to as a sales lead or just lead

lead : the identification of a person or entity that has the interest and authority to purchase a product or service.

A person or agency that provides leads is called a lead generator.

So you might say that John is the lead generator for the agency. However I think that sounds a bit stilted and would probably just say that John consistently produces the highest quality leads for the agency. Or something like that. Note though that this is a general business term and is not specific to real estate.

Solution 2:

If we were talking about journalism, you might get away with source, but I don’t think that quite works here. Try informer or adviser, or maybe local expert. My own personal favorite, though, is consultant.

A whistleblower gives information about an organization that is doing something underhanded or wrong. The whistleblower is the good guy, and the people he is reporting on are the bad guys. The negative connotation is that this makes a whistleblower something of a tattletale or snitch in the eyes of the organization he is informing on — that is, a fink, or even a rat.

A tipster has the connotation of himself being a bad guy, giving away valuable inside information that would not otherwise be available to the general public. Think of insider trading, for example.