'You can't just run around killing goblins and looting temples, this isn't the old days my boy. To make it today you've got to be part of the guild, and you need a team, and a look, and most importantly you need a manager. Like me.'
A new substance is found in an out of the way area and kept very quiet. It is found to make a perfect counterfeit diamond. Only the most expert of expert appraisers would even have a hope of noticing that it is fake. Only one problem: if it gets wet it starts to slime and if it is saturated, it turns into a glob of gel.