One possibility is to drop the best and the worst results, like in a diving contest: http://en.wikipedia.org/wiki/Diving#Scoring_the_dive

To reduce the subjectivity of scoring in major meets, panels of five or seven judges are assembled. If five judges then the highest and lowest scores are discarded and the middle three are summed ...

Also, make them play 100 games, and drop 10 of them.

This may work if it is a fast paced game. If it is slow paced with a complex strategy, then a good player may play like in a chess simultaneous exhibition http://en.wikipedia.org/wiki/Simultaneous_exhibition