If you say you’re working on reversing entropy people are more likely to believe you than if you say you’re working on a perpetual motion machine. Perpetual motion has had too much bad press. There’s a private school for training con artists that teaches things like this. Appeal to your mark’s better nature. Avoid publicity. Act normal. Try to keep everything you say interesting and believable. There’s a whole department of financial scams, and another for internet scams. Nobody applies to this school; somebody needs to refer them. If you know people who know, then you might get a call. It’s up to you to decide whether it’s a con.