The amount of trophies you win or lose depends on how many trophies your opponent has. Winning against an opponent that has the same amount of trophies you have will give you 30 trophies. If the opponent has more trophies than you, you will earn more than 30; if he/ she has less trophies than you, you will earn less than 30.
Similarly, if you lose against someone with more trophies than you, you will lose less than 30 trophies. If you lose against a player with fewer trophies, you will lose more than 30 trophies.
Similarly, if you lose against someone with more trophies than you, you will lose less than 30 trophies. If you lose against a player with fewer trophies, you will lose more than 30 trophies.