I never speak to anyone when I enter a room unless they say something before I get to the quest machine. I head right for the quest machine and up pops the quest. I wouldn't know if they were talking to me or not.
If you want to stop mules from overrunning your quest then make sure that your good prizes are not in the top ten or so spots. Then they will not have any idea where there ranking is at and at the same time you will be helping those who are not good at quest or have a hard time with their computer. This will help those to have a better chance.
Another thing to do would be to make your quest longer time wise. If your scared of someone playing ten players and your quest takes a half a hour or more to do, do you really think they will stick around and keep playing all there mules through it.
If you want to stop mules from overrunning your quest then make sure that your good prizes are not in the top ten or so spots. Then they will not have any idea where there ranking is at and at the same time you will be helping those who are not good at quest or have a hard time with their computer. This will help those to have a better chance.
Another thing to do would be to make your quest longer time wise. If your scared of someone playing ten players and your quest takes a half a hour or more to do, do you really think they will stick around and keep playing all there mules through it.