Settlers will cover for each other, and why not eh!? So the solution for this problem would have to be more Machiavelli. For the minority settlers who are price taggers, if they do not come forward, then their entire settlement gets blockaded, enough food and water for an existence nothing more. That will cause the others who are quiet to out the trouble makers. Of course its inhumane but these are settlers, troublemakers.. so who really cares except maybe them. Shut the settlements down.