The following is a guide to wipe out all data on the samsung galaxy S III (T999, I747, I535) and reset it to factory settings. I've tried it personally and it worked for me.
- Power off the phone
- Press and hold VOLUME UP and HOME button
- Press power button to power on the phone. Release the Power button once the phone vibrates.
- Release all other buttons once you see the andriod logo.
- Select Wipe data/Factory reset with VOLUME DOWN button. Press Power button to confirm.
- Select Yes - delete all user data with VOLUME DOWN button. Press Power button to confirm.
- Select Reboot system now to reboot the phone after the process is done.
- Congratulations, you now have factory reset the Samsung Galaxy S3.
Did it work for you? Please leave a comment on how it worked out for you.