Obviously, the very prohibition of weighing and measuring short makes weighing and measuring in full necessary. But, to emphasize it further, Sayyidna Shu'aib علیہ السلام said:
وَيَا قَوْمِ أَوْفُوا الْمِكْيَالَ وَالْمِيزَانَ بِالْقِسْطِ ۖ وَلَا تَبْخَسُوا النَّاسَ أَشْيَاءَهُمْ وَلَا تَعْثَوْا فِي الْأَرْضِ مُفْسِدِينَ
And 0 my people, perfect the measure and the balance with justice and do not make the people short of their things, and do not go about the earth spreading disorder - 85.