Yeah, the contest thing can get complicated fast!
Anyone can start a contest, of course, offering some sort of prize is an enticement, but even just naming someone a winner could be motivation enough. Basically, whoever starts a contest can invite anyone to judge, if they want a panel. They should commit to critiquing every mix submitted, and take the time to give actionable feedback, if they are technically capable, or at least subjective feedback of the sort you get from clients ("I like it but the snare feels too fat, can you make it have more whack?")
The main thing is committing to:
-Give feedback on every mix
-Set end end date for submissions
-Select a winner (and be prepared to defend your choice!)
Providing references will help make the judging process easier and a little more objective.
If you start a contest with a prize, let me know and I'll be sure to promote it with a banner, etc, too!
I'm also still working on future contest ideas, once the Mike Senior contest is officially in the bag!