If the item you have purchased has a defect and is found after purchase and delivery, it can be changed even later than the legal 30 day period. This exception is possible if the item sold has a ΄΄Hidden Defect΄΄ and / or ΄΄Industrial Defect΄΄.
Really in the general context of commerce, any weakness can not be identified before the sale from the moment the transaction takes place on the internet. For this reason, the buyer can not check the product, and can not be blamed for negligence. On the other hand, the seller can not be blamed for a defective product once the whole sale process is automated.