How to know if my iPhone 6s is brand-new?

I exchanged a defective iPhone 6s at T-Mobile and the one they gave me had multiple iCloud emails. It kept asking me for a password to sign in to the App Store, and the box has a "restocking fee applies when returning this product" sticker on it, and it was under the plastic I think, I m not sure. The day give me a brand-new iPhone or the day repackage a used one they fixed up and gave it to me? Like refurbished or something. When I looked at the battery it said it was three hours on standby. I m thinking of heading over there and asking, what should I do? I paid for a brand new one less than a week ago I shouldn t have an old one they fixed up just because it s defective, it s not my fault.
Added (1). The packaging was brand new, like the same as the one I got originally, except for that sticker. It doesn't say Apple certified or like new or whatever it's seemingly brand new

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