How to I identify a Fake iPhone 15 Pro?

I bought a phone today from a private seller at 711 so they said they where traveling across the country ran into somtroubles and needed cash asap the phone was in an unopened box stating 15 promax 1Tb . So I end up buying the phone and the apps were pre installed and they just look slithery off the phone seems super glitchy too I’m not really an Apple guy but I want to be can anyone help?

[Re-Titled By Moderator]