That exact same thing happened to me and DH (well, he wasn't DH then) back in college at an Elton John concert!!! It was amazing!!! We hadn't gone to our seats yet (we were near the top row, behind the stage), and we were looking at merchandise. Someone from the show came up to us and asked if we'd like to trade in our seats for front row. Told us we would just have to hand over our tickets bc they were going to give them away to people outside who didn't have any at all (sold out show).
I feel awful now bc I was not very nice to this guy. I thought he was trying to scam me for my tickets (yes, he had credentials, but I thought they were fake), and I made him walk with me to an usher, hand the front row tickets to the usher, and have her verify that I would actually be allowed to sit in the front with those and they weren't counterfeit. LOL. The guy thought I was NUTS I think. It was an amazing concert though!!