Once I was looking at a Remington 870 Wingmaster shotgun at a local sporting goods store (not a chain store). The guy checked the inventory book, and the gun had been in stock for six years! (It was a 28-gauge, which might be why it hadn't sold.) A lot of moving, bumping, smudging, etc. can happen in six years.
Sometimes, used guns that were purchased new-in-box and kept pristine by really "anal" owners are in better condition than "new" guns that were on display in busy gun shops. If you're having a hard time telling if your gun is "new," it probably is. No dings, dents, rust spots (all of which I've seen on "new" guns)? Congratulations: you've got yourself a new gun.