Fist off, try to establish a "real identity" before you send money.
Get the persons "real name", address and phone number. Check it out on Canada411. If you can verify phone number and address, you have a good starting point if you are subsequently ripped off.
Talking to the person on the phone goes a long way in dispelling any uncertainties. You can get a pretty good "feel" for the other person when talking live on the phone. Most scammers don't want to talk to you "live".
Rely on the other persons "feedback". If they have a +10 positive feedback, then have been trustworthy at least 10 times!
The police will persue folks who commit internet fraud. But if you send cash in an envelope to a P.O. box, then chances are you are screwed from ever getting your money back.
Use "common sense" when dealing on the internet. I have done a few deals on CGN and over 175 deals on eBay for non-gun stuff. Never been ripped off.