How They Do It: Craigslist Scams

As a frequent user of Craigslist, I always receive the emails asking me to ship something so somewhere in Africa because the buyer is giving it to their brother or some nonsense. If you have ever posted something on the website you likely know what I am talking about. They always offer to send you money through paypal and have you ship the item to one of their relatives in a foreign country.
If paypal is so secure, then how do they scam you? I recently found out how this works. Its quite simple really. They paypal you the money and desperately hope that you ship the item immediately. Paypal takes a certain amount of time to process and verify the payment ( I believe it's 24 hours), but you have access to the money immediately so it looks like they really paid you. You see that you have the money so you go ahead and ship the item thinking that everything is fine. The scammer will then send paypal a note and cancel their transaction. They get their money back and/or paypal can't verify the payment and the money is then withdrawn from your account leaving you without your payment and possibly in the negative. You get screwed and they get your item for free.
So be careful with who you deal with on craigslist or similar sites. I always recommend meeting face to face in public places (I like Sheetz where there is almost always a cop outside) and doing cash only transfers. That way you don't get screwed on the money (unless they have really good counterfeit bills) and hopefully since you are in a public place where lots of people can see you they will think twice about pulling a gun or a knife on you.