1. Does God accept all kinds of repentance without reckoning or punishment in this world or the Hereafter? 2. If I tarnished someone's reputation with words he did not say or do in front of another person, and I cannot rectify the matter, what should I do, and will God forgive me for this sin?

Sincere repentance that is accepted, with its conditions, erases the sin, and its perpetrator is not punished, neither in this world nor in the Hereafter. As for unaccepted repentance, it is that which does not fulfill its conditions, or occurs after the soul reaches the throat (death throes), or after the sun rises from the west. Among the conditions of repentance is fulfilling the rights pertaining to people. So, if the sin is related to slandering a person, then one must seek their forgiveness or clarify the truth to those to whom the words were conveyed. If that is not possible, then the repentant person should frequently seek forgiveness for that person and mention them positively.