Is it permissible for a shop to dispose of customers' jewelry—by melting and using it—if they do not come to collect it after the agreed-upon period of three months, given that there is a tolerance that sometimes extends for years?

If the shop owner stipulates that jewelry must be collected after 3 months, and its owner does not come to collect it, then the shop owner should take his fee and donate the remainder in charity, or sell it and donate its price in charity, without taking ownership of it. Sheikh Ibn Uthaymeen was asked about clothes left at a laundry after the stipulated period, and he replied: If it was stipulated to the owner of the clothes that if he delayed, he would have no right to them, then it is permissible for the laundry owner to donate them in charity or sell them and donate their price in charity. However, it is preferable to wait ten or fifteen days after the (stipulated) period. If there was a specific deadline between them, then once the deadline expires, he should donate them in charity or sell them and donate their price in charity. But if there was no specific deadline, then he should not sell them until despairing of their owner. It must be noted that gold intended for exchange is not permissible to keep in the shop; rather, the exchange must take place in the same sitting, hand to hand, like for like.