No wrong perpetrated on another person is justified by the wrong they did to you. You are responsible for your actions independent of other people’s actions.
Learn to recognize the childish voices in your head telling you that the other person started it or you had a right to hit them (literally or figuratively) because they struck you first. Learn to recognize the voices for what they are: immature attempts to justify a wrong you committed.
Practicing the forgotten art of repentance places you in the position of power because you are the one who controls the direction of the conversation. By doing so, you might be able to get the conversation back on track toward a productive end, such as a sale or a reconciled relationship. Asking for forgiveness is not displaying weakness, but strength. You are the one taking the more mature approach to ending the conflict. Even if the relationship goes no further, you have the knowledge that you did the right thing.