This is already the case currently. Once scams are identified as such, then they are eliminated. But the problem of course is that scams start off as seeming legitimate. That's the definition of scam, something that appeared legitimate but wasn't.

Even in "anarco-decadent" societies, scams would not flourish once they are revealed as scams because, why would anyone participate in something with a 100% chance of them losing all their money? The scammers may not face punishment from an overseeing authority like the state, but may very well by individual victims of the scam. Either way, scams can't continue as known scams in any arrangement of society. edit An exception to this is a fully corrupted authoritarian society. In this special case there could be 'approved scams' by some officials or people in power that everyone knows to be a scam, but they have to go along with over fear of violent reprisal.