Praise be to Allah.
If a product is sold subject to the condition that it cannot be returned or exchanged, that is not permissible, because it is an invalid condition which may lead to harm or confusion, and because the intention of the vendor in stipulating this condition is to oblige the purchaser to keep the product even if it is faulty. This condition does not exonerate him if faults are found in the product because if it is faulty then he should exchange the faulty product or the purchaser should be given a reduction, because the full price is given in exchange for a sound product, and if the vendor takes the full price when the product is faulty, he has taken it unlawfully.
According to sharee’ah, customary conditions are as valid as verbal conditions. Customarily it is assumed that the product will be free of faults, so the purchaser is justified in returning it if it is faulty.
And Allaah is the Source of strength.