I think the principle includes a certain degree of deterrence as well as inconvenience to the victim. Calculating exactly the right punishment is, of course difficult. That's what courts are for.
Well, most libertarian government structures call for precisely that. A police to enforce the law, a court system to provide fair rule and a small military intended for defense.
[edit: Should add that although there are certainly disputes to how to fund said services, to the best of my knowledge it's largely agreed that some court system is required.]