In Scandinavia, usually just by showing the "payment sent" screen to the merchant. The merchant can check their own device for the notification if they want confirmation.
Seems a bit slower than NFC, but I haven't seen it in action
(and the payment sent screen can be spoofed)
For tips it seems fine
For most situations, spoofing a sent-screen that usually displays the vendor or persons name, is not too easy to do in the heat of the moment, without preparation, so it's not really been a problem yet.