How is zakat paid on used spare parts that are still functional and can be sold, but are difficult to sort and determine the value of each part, knowing that they were not purchased but left behind by their owners?

Zakat is obligatory on everything prepared for sale, whether new or used, based on the Prophet, peace and blessings be upon him, saying: "He commanded us to give charity from what we prepare for sale." It is a condition that the Muslim owns these trade goods with the intention of trading. Therefore, these goods must be appraised when a year has passed, and one-quarter of one-tenth (2.5%) of their value must be paid. If precise appraisal is difficult, an approximate estimate is permissible with caution and an increase in the amount to ensure the discharge of one's obligation, and the excess is counted as a voluntary act.