Is it permissible to purchase goods from China, store them in Europe, and sell them online without possessing them, given the possibility of the buyer returning the goods and reclaiming their money?

If you purchase goods and store them in warehouses in Europe or elsewhere, it is permissible to sell them directly or online to any buyer, provided that the goods are permissible and do not involve deception. The option of inspection (khiyar al-ru'yah) for the buyer is permissible. It is not a condition that the warehouses be in the seller's country; rather, any recognized possession of the goods before selling them is sufficient, such as transporting them to warehouses where you have the right to store them.