alt Hacker NewsThat's a completely separate issue. It's got nothing at all to do with the currency being used. USD has exactly the same problems, as does every other currency on earth.
Society's answer to that is violence. More specifically, the threat of violence. If people don't do what's expected of them, at some point people with guns will show up and the violence will commence, and it will continue until the desired order is restored.
Stuff like laws and courts are just extra steps towards that violence. No matter the context, the threat of violence looms eternal and that's what makes people behave reasonably.
There is no threat of violence if the trading parties maintain anonimty. And even if they don't, there is little realistic threat unless the victim can prove to authorities who the offending party was.