Firstly, we see the chances given on a 1X2 guess and verify which group is the favorite to win. Normally Lower odds are given on the group that is more likely to win. Secondary we see statistical analyses of previous matches to determine if the odds for 1x2 are appropriate.
Take the instance of Rafael Nadal's assembly with Benoît Paire on the clay court of Roland Garros, for which Nadal is favourite. In this context of complete domination of the Spaniard on the French Open, it seems clear that essentially the most reliable prediction shall be his victory, to the disadvantage...