Just like being in the real world. Make smart decisions to the best of your ability and you'll be alright. There's nothing inherently wrong with the internet. Some people have things inherently wrong with them, and some of those people use the internet. Nothing to see here.
Wow... I had only ever used Craig's List for buying and selling goods. I had no idea there were people raping and murdering each other on there. You'd think that the admins would try to put a stop to that.