When you show integrity in dealing with the other person irrespective of the negative implication it might have for you, you are creating a long lasting goodwill which shall pay multiple times. It may take months and years but it never goes in vain. You don’t have to be fair in expectation of future rewards. It should be a natural phenomenon and attitude of doing the right things. Some may consider this foolishness. It is them who will consider you smart in the long term.