This is not an exploit because the person was in your guild and they joined the guild war party. Limiting your members to being high ranked and strong to the party only is a fast track to having people not want to be in your guild. This was just a person being a bad sport.
Good lord, that's completely ridiculous. Wouldn't it be better just to.. -looks up at the quote chain- .. who the heck would pay over 200m on a sword?!