So let's say there's a person in the Sect of Blades that wins every duel they challenge or accept, period. I'm not singling anyone out, since there's multiple people that have been in this position over time. Due to the anonymity of sect challenges, and due to the fact that everyone in the sect can accept a challenge at any time, this means that there's a significant chance of a person being paired up with this totally undefeatable guy. It's driving players to actually ignore sect challenges and not challenge at all, because they know that that one guy that absolutely nobody can beat is going to accept and win. Since you don't gain marks for losing, and you don't gain experience by being defeated by someone over and over again whom you have no chance of besting, there is absolutely no incentive to sect challenge/sect accept when this one particular person is around, because everyone knows they are going to lose against this guy no matter what they do.
How do you solve this problem, and make it so that people can actually enjoy participating in Sect of Blades fights again without having to worry about one completely unstoppable guy accepting and winning every single challenge no matter what?