Barcode number re-sellers are companies that have bought barcode numbers off other companies and then try to on-sell the numbers.
GS1 has no relationship with these re-sellers, so we can't provide guaranteed information about whether the re-sellers are trying to sell you legitimate, authorised numbers.
We can't know if the barcode numbers they provide are unique against other numbers directly allocated by a GS1 organisation. Also we can't validate these numbers for eCommerce, as we have no means of tracing who the numbers have been assigned to.