How to know my iphone 7 is new or refurbished

While Apple does not publicly acknowledge the different model numbers, it is known, based on anecdotal evidence over the years, that model numbers starting with the letter F are indicative of refurbished units by Apple.

Models - The iPhone Wiki

An Apple refurbished unit, is indistinguishable from a new one, and is refurbished with all new backs and and screens, along with any internal component that may need replacing. In other words Apple basically re-manufactures the iPhone so it complies with their strict standards, and further tests the refurbished unit to make sure its in perfect working order. Refurbished iPhones carry a full one year warranty and just as good as a new device.

Apple does not sell refurbished units to shops or stores, it only sells them directly themselves through their online store. So the only way the shop got a hold of a refurbished unit is from another person that got it from Apple or by buying it directly from Apple.

Refurbished iPhone - Apple

If the shop passed it off as brand new iPhone, then they lied, but not sure there is much that can be done at this point.

The link for the iPhone Wiki I provided above has the identification of the possible first letters and their meaning. https://www.theiphonewiki.com/wiki/Models

did you buy from an Authorized Apple Reseller or somewhere on line?

Check Your Service and Support Coverage - Apple Support

If you’re paying full price anyway, there is no reason not to buy direct from Apple, or an Apple Authorized seller and avoid any such concerns. By definition, non-Apple Authorized sellers have no access to Apple’s retail new stock supply, so anything and everything they sell you is at the very least, a technically used device (i.e. it cannot possible be a truly retail new device since the seller has no legitimate means of getting such stock).

You forgot one important point. In egypt as example you will find many many small mobile shops. They have most the time some new iphones. This iphones come from all over the world. There are tourists selling them to the shops, plus family members who send them to the shops from the places in Europe and America they live. So many times the mobiles are ok but without warranty offcourse. Because the warranty only grips in there origin country where the mobile was sold. But there are offcourse also official apple retailers.

I’m not missing anything. You can find the same thing in any USA city. Pawn shops in particular will have unboxed iPhones (but still, used, as they’ve been sold at retail somewhere) But why buy a used phone at full price when you could get an actual retail new phone for the same price and from an Apple Authorized seller? That makes zero sense to me.

No non-Authorized seller has retail new phones. Everything they have is, if not outright stolen merchandise, used devices. They have no access to retail new devices through Apple’s supply chain.

Where, exactly, did you buy the phone? Why are you concerned as to whether it's new or not?