Genuine or fake product?

A simple test is to open the App Store. If you get either of these results:

1. A message the app can't open, or can't connect to the App Store when anywhere else online works.
2. You end up at the Google Play store.

Then it's an Android phone made to look like an iPhone.

If it does connect to the App Store, it's real. Only Apple devices can succeed with this connection.

See: Check your service and support coverage - Apple Support

That would get device information from serial numbers.

Why do you doubt it?