1 physical product (not class of products) = 1 barcode = 1 identification

E.g. in web system you can assign owner to barcode (product). Different scenarios if owner is known before purchase or assigned later. All other trials to validate product id as unique should fail and client might request return of money.

or what if there exist many goods with same unique barcode, scattered around the world.

this requires a mean to identify where the unique good is (if it exists at all). would rfid fix this? hmmm shrug