Put in a humongous case so you can't enjoy the pristineness until you resell it.
Even then, if it's in pretty good condition overall, it will sell faster jailbroken/unlocked than 100% mint and stock.
Right from the get go, you should have paired the Bumper with an Invisible Shield for the back and front. No scratches, no anything.
I wouldn't leave the AT&T store until the associate put the Zagg front and back on for me.
Marc