I find that if you do too awesome in ANY game, you will get a crappy sapphire. Or a ruby.
So to get something better you have to get ABOVE that already super high awesome score. Like getting 80,000 + in magic pop (yay, black diamond). But if you get 60,000 you get a sapphire.
But yea, it's really annoying and disheartening. It makes you feel like you dont want to do it anymore.