Using ShipStation's Branded Returns Portal allows your customers to conveniently return items without the delay of waiting for you to first authorize the return. This is made effective by ShipStation's Returnable product option. This is an item-level option that you can find on the Product Default. By default, this setting will be enabled.
Perhaps you have certain products you don't want your customers to return. Maybe you'd prefer further feedback about why the customer is returning the item, etc. prior to authorizing the return. Deselect the box on the product default to make a product non-returnable. Or update this field in bulk via importing an updated Product CSV. (Download a sample of the CSV template here.)
When a customer tries to print a return label for a non-returnable item via the Returns portal, they'll receive an error that reads, "This item is unable to be returned":