Not true. If I sell my tickets on ticket exchange it voids my paper tickets and reissues a new bar code. If I try to go in with the physical tickets, mine won't work, only those that were issued to the buyer.
Back in the day, I used to list games on ticket master ticket exchange and stubhub. I accidentally sold the same game on both sites. The guy that bought them on stubhub got screwed- until I gave him 150% return and tickets to a game of his choosing.