How can i know if my iphone had an owner before?

I would start by submitting the serial number at Check Your Service and Support Coverage - Apple Support and see if the dates are correct for supply to you. Finding a date earlier than you received your phone is an indication it is not new.

However, it does not matter because the device supplied was damaged before you received it, so you should reject it and demand an undamaged replacement.

The lack of battery does not mean its not new.

Unless it cannot be charged, the lack if battery just means it may have been sitting in your carrier's wearhouse for a long time and the battery eventually drained.

Yes, normally iPhones have some battery when taken out of the box, but its not completely unheard off to get iPhones without any charge.

There's no way to prove it has been used, and no reason to think it has been used. Again lack of battery does not mean its used.

The scratches on the screen may indicate a refurbished device. Unless you can prove the scratches were made before it was taken out of the box, the carrier may not want to replace it.

You can take it to an Apple Store, and see what they say.