What is the ruling on advertising a product while concealing its price, then offering a discount on the price after a period to a customer who has not purchased it? Is doing so permissible? And does compensating customers for products proven to have a defect after they were sold, when hundreds of pieces of them have been sold, absolve one of responsibility before Allah?

There is no harm for the seller in lowering the price to attract a buyer, provided there is mutual consent between the two parties and falsehood is avoided. As for a defect that the seller was unaware of, the buyer has the right to annul the sale or to take the 'arsh (compensation for the defect) according to the Hanbalis. This is the preponderant opinion and is suitable for online sales. However, according to the Shafi'is, the buyer is not permitted to keep the defective item and take compensation for the defect; rather, he must either return it or keep it for the full price. As for buyers who did not inform the seller about the defect, the questioner is not obliged to clear his financial liability to them because the default is innocence until liability is proven with certainty.