A pattern that repeats is for a person to build up trust and then once enough trust has been reached use that to scam and then abandon that profile. Anonymity makes that cheap and easy to do.
Even knowing the person's real-life identity isn't protection -- as we know from pirateat40's ponzi scam.
The Bitcoin-OTC Web of Trust (WoT) is also vulnerable to that however it can be longer in duration and can span communities.
When dealing with non-reversible forms of payment, essentially there are no guarantees and limited recourse. That's the nature of these instruments.
Some effort can be made to make it clear your counterparty is not in it to cut and run. Here's an article that explains how this is nothing new:
- http://theumlaut.com/2013/02/27/bitcoin-and-bank-architecture/
And here are some resources:
- http://en.bitcoin.it/wiki/Secure_Trading
- http://wiki.bitcoin-otc.com/wiki/Using_bitcoin-otc#Risk_of_fraud