You should exercise the same caution on the net that you use in real life, of course. If someone seems too good to be true, they probably are. Don't believe everything you read. Evaluate the consistency and integrity of their story. And in the end, most people, even intelligent, thoughtful, experienced people, can be taken in by a really, really good scam or con.
Some people are just very good at manipulation and lying, and they can fool even astute people.
The guilt is with the manipulator, with the con artist, with the liar. As for those people who use the net to hurt or manipulate others, get a friggin life, you losers. It may not come around today, but it will come around. If you plant bad seeds, you're gonna have a nasty harvest. Getting off my soapbox now.