In Buddhism you do evil you just are expected to do it no more or karma will get you.
Karma
will get you. If you do it again then karma will get you again.
Then you will keep on suffering, dying and being reborn until you do care. Buddhism is a universalist religion; everyone attains nirvana eventually.
Can we also be evil without getting our just desserts?
No. Karma is unavoidable. Karma does not forgive and karma is not arbitrary. If you do the crime then you do the time.
How does Buddhism explain fairness? GOD explains it clearly.
To a Buddhist, Christianity does not seem fair. Calvinists tell me that my actions have no effect for good or bad. God has already decided if I am going to heaven or hell and nothing I can do will change that inevitable fate. I do not see that as at all fair. Alternatively God might (or might not) forgive my sins, but that is God’s decision. Again that does not seem fair to me. In both cases there is a disconnect between my actions and the results of my actions. How can such a disconnect be fair?
So there is no guaranteed penalty for being evil?
In Christianity, no there isn’t. In Buddhism yes there is. Reward and punishment are both guaranteed in Buddhism. In Christianity God might, or might not, intervene and so there is no guarantee.
However, if we choose to follow GOD’s instructions, we have faith that we will be rewarded with eternal life
You are making a mistaken assumption here. To a Buddhist eternal life is eternal suffering, whether in one of the heavens or in one of the hells.
Consider, you are in a luxury five-star hotel room, being pampered with top-notch service. In the room next door your family is screaming in pain as they are being tortured. You can hear them suffering horribly. Are you happy? Of course not. All Christians and Buddhists love their neighbours. As long as even one neighbour is suffering in hell, how can you be happy in heaven?
Christianity guarantees evil will be punished to the fullest extent of the law and will no longer be tolerated. Does Buddhism give us anything to match this?
Christianity gives no such guarantee, as I pointed out above. Buddhism does give the guarantee. Karma does not forgive. Karma does not decide beforehand.
rossum