The advice may sound tired, but it is still as valid today as it ever was: "If something sounds too good to be true, it probably is."

And now this maxim applies even to financial proposals that reach out to investors who want to put greenbacks in green-tech. Here is a story ripped straight from the SEC website:  "Four individuals and two companies were charged with perpetrating a $30 million Ponzi scheme in which they persuaded more than 300 investors nationwide to participate in purported environmentally-friendly investment opportunities."