[...] First lie to yourself about what grade the diamond is; then you can sincerely tell your customer "the truth" about what it's worth. As I would tell my salespeople: If you want to be an expert deceiver, master the art of self-deception. People will believe you when they see that you yourself are deeply convinced. It sounds difficult to do, but in fact it's easy -- we are already experts at lying to ourselves. We believe just what we want to believe.