Is it obligatory to inform the buyer of any defect or shortcoming in the sold item, whether it be a car or a program, and am I required to re-improve the product (program/script) even after delivery if a better method is found? And must I choose the best security or organizational method in programming even if it requires more time and effort from me? And is saying "the cheapest on the market" or advertising "Red Bull gives you wings" considered a form of forbidden deception or misrepresentation?

What is prohibited in selling is the concealment of defects that reduce the price or prevent the buyer from achieving a legitimate purpose. The definition of a defect according to the Hanafis and Hanbalis is that which necessitates a reduction in price. According to the Shafi'is, it is anything that reduces the object or its value in a way that defeats a legitimate purpose. According to the Malikis, it is the existence of a defect in the sold item or the price. The reference for knowing effective and ineffective defects is to experts. The fundamental principle for a hired worker is to perfect their work and for it to be free from effective defects.