Is it forbidden to return devices to the place of purchase after their price has decreased, knowing that the website's policy allows returns within 14 days?

If the website allows the buyer to return the item within 14 days, whether it is defective or sound, this is considered a stipulated option (khiyar al-shart). You are permitted to return it due to a decrease in its price. It is permissible to stipulate an option for a known period, whether short or long. However, offering the item for sale during the option period nullifies your option according to the majority of scholars. In contrast, the Shafi'is and some Malikis and Hanbalis hold that offering it for sale does not nullify the option, and Sharia standards have adopted this view. However, if the website only allows returns due to a defect or a difference in description, then you are not permitted to return the item simply because its price has decreased, but only if there is a defect or a lack of conformity to the description, based on the Almighty's saying: "O you who have believed, fulfill [your] contracts" (Quran 5:1), and the Prophet's (PBUH) saying: "Muslims are bound by their conditions."