When a customer returns an unsellable item you can request Amazon to return it to you and they will charge you per unit. This is recommended so you can examine the inventory and resell.
You can also request Amazon to dispose of inventory for a small price per unit. This means you relinquish control over the returned item and Amazon becomes the owner. They can sell it as “used”. They can also auction large bins of random “disposed” items that liquidators will purchase and resell.