This is what a man or woman is when they know their self worth. They will not settle for less. Someone that has set their standards high. Those standards are respected only because those that want the man or woman in question know they are getting something that everyone wants, but can't have.
For instance, there's a woman who knows exactly what she wants and more importantly, deserves. A woman like this is a high commodity. Surely a "real" man does not want someone who is not sure of herself. Therefore, the woman is most likely wanted by several men and therefore, is "high real estate."