I just flashed my s3 back to factory stock and did a factory reset. Before doing this I had an unlocked bootloader. I never re-locked it before going back to stock. Is there a way to tell if it is still unlocked before I return it? Seems to me I read somewhere that when you start your phone and the "SAMSUNG" image flashes very briefly it means you are unlocked. Mine does just that even after flashing back to stock.
I'm 98.5% sure if you're Odin your phone back to stock unrooted EVERYTHING (including your bootloader) will return to a factory state.
I know this because I've tried several ROMs w/ kernels and have returned my device to stock quite a few times.
Don't jump through hoops unless they person giving you advice has done it themselves.
Sent from my SCH-I535 using Android Central Forums
I was rooted and unlocked, used ODIN to flash back to the factory rom and was still unlocked after a complete reset. You can tell by how long the "SAMSUNG" stays on the phone at boot-up. If it is a quick flash of about a second then you are unlocked, if it stays on the phone for more than a second or 2 you have a locked bootloader. Watch an unboxing video to see how long it should stay on the screen. I had to re-root my phone and re-download EZUNLOCK and re-lock the bootloader and then ODIN back to stock and was good to go.