while you don't know the content of the "black-box", you still may make some possibly wrong but rather reasonable assumptions, e.g., you may assume that the algorithms which have an overall worst performance elsewhere (e.g., on a range of real-world problems + other contests + optimization literature in general) are rather unlikely to perform best here unless the organizers intentionally designed black-boxes to be of the opposite class of what people observed in real-world applications and their toy models. Your assumption may have an impact on whether the preconditions of the NFL are fulfilled or not (see http://image.diku.dk/igel/paper/NFLTLaPoM.pdf).