This should be pretty clear and self-evident without explanation, but to make sure this is well-understood:

Dueling is intended to be a PvP experience between two specific people, represented by two specific characters/accounts. This is why we have a duel ranking system, to illustrate the relative outcomes of these battles, and help players measure their skills against one another.

Two individuals colluding to switch places on one account, so that a relative newcomer who is poor at fighting can then switch out and be replaced by a very strong and experienced player, is considered to be "Fraud", as defined by Section 1.1 paragraph 4 of the Vendetta Online Rules of Conduct. It also damages our entire duel-ranking system, in ways that are challenging to fix, and is generally bad behaviour.

Now, if a single individual wants to roll a new alt-character, and try to behave like a newbie for a long period of time, and pretend to be bad at fighting, and then duel someone and surprise them with their actual skills.. fine, we aren't currently going to raise an issue over that. It skims too close to variants of Role Playing.

But two people colluding together and sharing a character, that crosses way over the line, clearly violates a number of well-known policies, and will receive disciplinary action.