If you buy a preowned Samsung Galaxy Note 4, you should ask the question in each case whether this device was "flashed" or rooted. Rooted means that the user can access system files and the kernel. Flashed means that a changed and not original Android software is loaded on the device. Neither is equivalent to the original Android and can lead to problems with the Samsung Galaxy Note 4.
Through a rooted device is the guarantee is lost. Due to the flash of a non-original Android software, it may happen, for example, that you will not get any new original firmware updates to your Samsung Galaxy Note 4. That is why you should always check before buying a Note 4 whether the device was subjected to one of the two methods above.
1. Is my Samsung Galaxy Note 4 rooted?
To test this, open the menu on the smartphone and then the settings. Scroll down to "Device Information" and tap on the entry. Next, select "Status" and then scroll down the list to the bottom. You should see the "Device status" box. The device status should show "officially". If it shows "modified" the Samsung Galaxy Note 4 is rooted and the Knox-counter has been set to 0x1.The guarantee is irretrievably gone.
2. Is my Samsung Galaxy Note 4 flashed?
This is not so easy to test. You can maybe recognize a flashed Android, that additional apps are installed or the launcher does not match the original. A popular software for flashing is Cynogen Mod. Information on your Android system can be found in any case here:
Menu --> Settings-->Device Information
Check here what the Android version and baseband version is. Compare this with the firmware which is currently available for the Galaxy Samsung Note 4. So you can get most of the flashed Android version on the ropes.
You now knowhow to check on the Samsung Galaxy Note 4,if the device is rooted or flashed.