This can be a bit tricky. Short of having the potential client sign an NDA, I am not sure that there is a perfect answer. LTsFolly makes some good points (I still don't trust those bats, though... ), in speaking of, and showing results, or potential results.
Now, I normally went into detail, on how the project would be structured, the potential shooting schedule, and then tried to stay a bit vague, only showing similar shots/projects, that they could relate to. Still, I had one potential client come back, after a very involved architectural project, and ask if I could tell the "semi-pro" that they hired, because of price constraints, how to create shots like my portfolio pieces, based on the proposed shooting schedule. Yeah, in their dreams!
I also see some potential clients, who offer to hold "contests," where creatives produce pieces, for the chance to work with them. However, I do see ad agencies making some very involved and highly expensive pitches to clients, only to have the contracts go elsewhere, and then the campaign looks suspiciously like one, or more, of those proposals. Guess that it boils down to ethics.
At a point, I just said the heck with it, and retired, to raise wolverines.
Good luck,
Hunt
