What makes you think a homeowner has any airspace?
The general principle is:
The Property Rights of Airspace - dummies
If aircraft can't fly below 500' (landing aside), then It would be interesting to see how a drone at 400' would be interfering (in a court argument, that is).
For the real estate agent - I'd like to see CASA prove that the pic was from a drone and not a crane... or a long selfie stick, or a kite, or ...