@Riger Eh. You might have missed it, but he B rank douche brought witnesses for the exact purpose of making it a duel. If there are no such witnesses and a person is found dead, another claiming it was a duel, it would likely be considered a murder instead. Duels often had witnesses, at least the seconds. A duel is a matter of honour and pride, after all. Not that the B rank scumbag would have a gram of honour, but he will learn his lesson in time.
Anyway, I already said the robbery part is too much.