All great advice given here.
I would reiterate, seeing the topography of built out lots in the area could be a big help. Also, within google earth, you can put the cursor on one side of the lot and then on the other and watch (at the bottom right had of screen) how the elevation changes. Keep in mind this has a margin of error, but can give you some idea of the drop.
Lastly, I would most definitely have someone go put eyes on it. A picture is worth 1000 words. And a video is worth much more. Not only for you, but for your future buyer.