For sports teams/venues that partner with them, they do.
When I sell my hockey tickets on stubhub, they place my tickets on hold with Tickets.com, and once sold, my physical tickets can no longer be used to gain entry to the event. The tickets that the buyer receives has a new barcode on them, so they can rest assured they won't have an issue at the gate.
When I sell my hockey tickets on stubhub, they place my tickets on hold with Tickets.com, and once sold, my physical tickets can no longer be used to gain entry to the event. The tickets that the buyer receives has a new barcode on them, so they can rest assured they won't have an issue at the gate.