In The Name of Allaah, The Most Merciful, The Bestower of Mercy.

Allaah [The Exalted] said:

وَيْلٌ لِّلْمُطَفِّفِينَ
الَّذِينَ إِذَا اكْتَالُوا عَلَى النَّاسِ يَسْتَوْفُونَ
وَإِذَا كَالُوهُمْ أَو وَّزَنُوهُمْ يُخْسِرُونَ

Imaam As-Sadi [rahimahullaah] said: This noble Aayah shows that just as a person takes from the people what he is entitled to, it is also obligated on him to give them everything they are entitled to – whether related to wealth or mutual dealings; rather included in the generality of this Aayah are proofs and statements, because indeed what usually takes place between those engaged in argumentation and discussion is that each of them is eager to establish his proofs, therefore, it is obligated on a person also to make known the proofs possessed by the other person and examine the proofs of the other person just as he examines his own proofs. In relation to this affair, the justice of a person is known as opposed to whether he is afflicted with bigotry, his humility as opposed to being haughty, his common sense as opposed to foolish behaviour. We ask Allah bestow on us every good. [An Excerpt from Tafseer As-Sadi]

Imaam Muhammad Ibn Saaleh Al-Uthaymeen [may Allaah have mercy upon him] said, “Fujoor Fil Khusoomah (Iniquity when disputing) is of types: Rejecting what is obligatory upon you (to fulfil, give etc) and claiming what one is not entitled to”. https://youtu.be/FGtZtOBbif4

Finally, beware of false accusation, because Allaah [The Exalted] said:

وَمَن يَكْسِبْ خَطِيئَةً أَوْ إِثْمًا ثُمَّ يَرْمِ بِهِ بَرِيئًا فَقَدِ احْتَمَلَ بُهْتَانًا وَإِثْمًا مُّبِينًا

And whoever earns a fault or a sin and then throws it on to someone innocent, he has indeed burdened himself with falsehood and a manifest sin. [Surah An-Nisaa. Aayah 112]