The valid winner comment will be voted up by @steemplayroom always and commented on. I did think about requiring people to vote, but I chose to go the other way this time to see how it goes. @Steemplayroom will always vote for the winner so delegating is an option, I hope as the service serves people over time, this will become more used option to ensure proper rewards.
Even though impersonating doesn't really work (someone already tried it), if it is repeated, they will get warned and flagged after that to keep comment section free of multiple winner replies.
Now that I think of it, maybe trail could be setup that votes for the winners only? I haven't looked into it so not sure.
I think required delegating is going to be the best solution but maybe(hopefully) people will surprise me and not take advantage.
Once the service is running as expected and is more fleshed out, I will consider requiring a small upvote to join the match.