Actually my question applies to any Apple product.

I am contemplating buying my friends 5S as he has been given a company iPhone and this 5S is surplus to requirement.

Question is, when an Apple product is reset to 'factory settings' can it now be registered 'as new' to another persons iTunes account without any issues?

Although this phone is Thai registered and all legitimate, I was also wondering also, when an Apple product is reset to factory settings, is there a way to check if its a bonafide unit for that country or whether its a grey market import?

Question. Is the phone registered / used with iTunes?

If so.

You first have to get the current owner to unregister it from their Apple ID. They need to do the following:

1. Go to: https://supportprofile.apple.com/MySupportProfile.do
2. Login with their Apple ID
3. Click on ">" to the right of the phone listing
4. Click "unregister"