Fundamentally, a confidence scheme is any system where overwhelming pressure is brought on the mark to concentrate on the outcome, x, rather than the expectation value, xp(x), where p(x) is the probability of the outcome.
The concept of scamming cannot be precisely defined and outlawed. It is essentially a form of opportunism, "self-interest seeking with guile."5 The voluntary participation of the victims and the challenges associated with identifying scamming often result in skepticism toward the plausibility of scams and demands that individuals would be responsible for the choices they make.
Maybe I'm a little out of my depth criticizing an article by two professors from a college of law, but how on earth can you attempt to define scamming without mentioning fraud? The con-man willfully misrepresents his part of the transaction despite knowing the mark to believe otherwise. And it isn't a matter of subjective degree. In the Nigerian Prince scheme, for example, there is no prince, and there is no diamond fund tied up in escrow. It's a complete fabrication. That's the difference between market persuasion and crime.