Personally I would like to believe that most people would not accept a check from someone they did not know in person. I'm not sure why they do it because the transaction takes place online. While I'm a strong advocate for using technology to help fight crime; lately I seem to be drawn back to some very low tech but savvy advice...
"If it seems to good to be true, it probably is." As well as the old favorite, use some common sense.
The biggest piece of crime prevention advice that I can give is use some common sense when you are going to do something. For instance, don't leave your irreplaceable laptop computer in the backseat of your car when you park in the mall parking lot. Another good piece of common sense is don't agree to accept ten times the amount you are asking for when you are selling something online, and then mail the difference back to the buyer.