If there was no SIM, it would have warmed you that there wasn't a SIM. Is it a Verizon model? They apparently can work without a SIM(?), although I have no experience with a Verizon iPhone.
Sounds odd. It's possible to re-shrink wrap something. Where I used to live, there was a guy nicknamed 'Dirty Dick', and he did all kinds of 'shady' things with parts, software, computers. But he had the best prices in used systems and hosted the Mac user group. And I think the way that Apple shrink wraps their boxes is rather unique and hard to duplicate.
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thanks for your reply but how would i know if it has been resealed, is there is any risk of using it, i mean for my personal data, fingerprint iCloud etc. i haven't tried with sim yet. i bought it from another country. thanks
You reset it, correct? That's about as good as you can do. You are probably good, but this is what happens when you buy from an unknown/insecure source. It's not like a gun where it can be traced to nefarious and lethal activity. Knockoffs, from what I've seen, are so obvious that you would know it pretty quick.
Possibly someone bought it, had it for a while, and swapped it, or traded it in on something else...