This story was relayed to me by one of my agents:
My agent accompanied a client on a rental showing which was being leased "by owner". Prior to the showing, there was some discussion with the homeowner about using a broker, and she dismissed it with a blase' remark that she could find her own properties, as if that's all a broker does.
At the showing, the owner showed the place herself, and in the ensuing discussion, asked my client a question. "Are you," she asked "___________?"
The "_________" is a protected class. Race, creed, status, is immaterial. You don't ask. Ever.
My agent and the client stood there in what I can only imagine to be a monumentally uncomfortable silence. As they both turned to her, the owner said, very matter of factly, "is it a problem that I asked?". The agent replied,"It is if you now turn him down".
This is not a one-time thing. Even in cases where owners showed their own home listed with a broker (we advise to leave the agent and client alone), I have heard some outrageous questions asked of the client. If the client is a Visigoth, the dopey owner wants him to know that another Visigoth lives down the street, or that the president of the PTA is half Hun. Dumb, dumb stuff.
Fair housing laws do not just apply to brokerage. They apply to anyone selling or renting a home. Anyone. And stupidity or ignorance are far more costly than my brokerage fee.