Android has a feature known as 'FRP', or 'Factory Reset Protection'. This is designed to prevent someone stealing your phone, performing a factory reset, then selling it on. If you don't do things in the right way however, this can also trip you up when selling your device (perhaps in our new Classified Ads area!).
What does this mean?
If you don't wipe your device in a 'FRP friendly way', when the new owner tries to use the device for the first time, they will need to sign in with a previously used Google account first - i.e. yours. Unless you want to be giving your Google account details out, this is not ideal.
When does this normally occur?
FRP is most commonly triggered when you perform a factory reset from recovery or bootloader directly.
How can I prevent this happening?
The key thing to do is ensure that you always reset your device from the settings menu. Anywhere else, any other way, you're at risk of tripping FRP.
OK, got it. Any other tips?
When I'm selling on a device, I always perform the reset, connect to Wi-Fi, skip through the wizard to the home screen to ensure everything is OK, then reset one more time. It might be overkill, but I then know that FRP is disabled.
Edited by PaulOBrien