Defrauding is to decrease the weight (balance) in case one is buying and has to pay money for the merchandise, and to increase the weight if he is the one selling.
Allah avenged the people of Shuaib, who were known for cheating the balance and the scale, which is when buying they will take more than what they pay for, and when selling they will charge the full price but give a lesser amount, therefore they would steal from the seller if they were buying, and from the buyer if they sold.
(Woe to the defrauders! Those who take full measure ˹when they buy˺ from people, but give less when they measure or weigh for buyers. Do such people not think that they will be resurrected. for a tremendous Day— the Day ˹all˺ people will stand before the Lord of all worlds?) Al-Mutaffiffin 83: 1-6
التطفيف هو النقص في الكيل و الميزان لمن كان له المال و الزيادة فيه لمن كان له الموزون.لقد انتقم الله من قوم شعيب الذين اشتهروا بتطفيف الكيل والميزان، وهو أخذهم السلعة زائدة الوزن، وبيعهم اياها ناقصة الوزن ، فكانوا يسرقون من البائع إذا باعهم، ومن المشتري اذا باعوه، نزل فيهم
قول الله تعالى: وَيْلٌ لِّلْمُطَفِّفِينَ ﴿١﴾ الَّذِينَ إِذَا اكْتَالُوا عَلَى النَّاسِ يَسْتَوْفُونَ ﴿٢﴾ وَإِذَا كَالُوهُمْ أَو وَّزَنُوهُمْ يُخْسِرُونَ ﴿٣﴾ أَلَا يَظُنُّ أُولَٰئِكَ أَنَّهُم مَّبْعُوثُونَ ﴿٤﴾ لِيَوْمٍ عَظِيمٍ ﴿٥﴾ يَوْمَ يَقُومُ النَّاسُ لِرَبِّ الْعَالَمِينَ ﴿٦﴾ المطففين 83: 1-6.