Article continues below advertisementThere are real estate agents. And then there is Harold Clarke.To most people, Hawai'i's luxury market is a place of postcard views and prestige addresses. But Clarke doesn't deal in what's visible. As CEO of MegaCapital Hawaii Corp.-a private office overseeing Luxury Big Island and Private Listings-he operates in a dimension of the market that few ever access, and fewer still understand. It's a structure built not for exposure, but for discretion.Clarke is not looking for reach or public recognition.