Fake or original

First thing - when you switch it on the first screen should say "Hello" in several different languages. Anything else, and it's locked to a user already, and if the seller cannot unlock it, walk away.

If you need to ask that question, you need to think about where you're buying it from. Hard to know how you'd tell. You need to have the phone in your possession for a little while to be able to tell. You probably need to be less concerned about it being fake than it being stolen.

the guy said that the phone is brand new, he didnt even unboxed it. so, i have to start the phone to see if everything is ok?

Guys say all kinds of thing to separate you from your money.

As is being suggested... if you can't touch the phone before paying, move on. far too many online sales are for stolen or previously lost devices. The risk is *very* high.

i can unbox it when it arrives to check if there really is a phone. and i wanted to ask how can i know if its not stolen or some replication. what do i look for?

It's not only that there is a phone... it's whether Find My Phone is enabled and the device is activation locked.

Best of luck if you take the chance.

Before you buy this phone, read this link --> https://discussions.apple.com/docs/DOC-250001038

If you can't see this phone in person, I would NOT buy it, no matter how good the deal.

You have been adequatly warned about buying from an unknown source because we do not want to see you back here asking how to defeat Activation Lock which is impossible.