Edit: After unsuccessfully attempting to 3 star the same level for 2 months straight, I have decided to uninstall this game, because I refuse to spend money on it, and that seems to be the only way to win. The cards are definitely stacked in your virtual opponents' favor instead of just making them more challenging opponents. Also, you can tell that there's usually one that's designed to do better in each of the levels where you have more than one opponent.