When I fought, I auto accepted challenges, and also did some challenging of my own. Some people did not accept my challenges, and after a couple of those I just waited for other people to challenge me. I figured at the end of the day it didn't really matter, because if there were people not getting into challenges, they couldn't die but they couldn't kill either. It would be pretty obvious who they were as the battle narrowed down - they would be the ones standing around not fighting anyone. And then they could be quickly disqualified.
I think manual-accept challenges with a rule that you have to accept them all would have been best, because then you would at least know who/how many are attacking you (which IRL you could, but lag and sprite-clipping made it too confusing IG). That would also stop people from suprise-attacking you without allowing themselves to be suprise-attackable.