You are a university student, prob on a shoe string budget hence looking for a use iphone, you have never used iphone before which means you were using andriod phones. Now you want a shiny iPhone to prove that you are better. Your priorities are so right.......
Maybe the OP wants iOS. Good advice in here already. There are no fakes. If you can call and sign in apple id, it's legit. But if you're trying to save money, getting a cheaper new Android is probably better choice.
I bought maybe 5 iPhones on appliu and never have issues. The only issue I have with apple devices where I've bought them new or 2nd hand is the lightning connector. It has a limited life time. So I buy these cables with magnetic cables for about HK$39. Brings the wear an tear of the iPhone to zero.
https://www.gadgetzoverload.com/prod...st-charge-2-4a Get the ones that are revesable so it doesn't matter how you connect it. Note that the magnets are fragile and they can shatter if you bang them.
I've had one where the battery was worn. The new IOS 11.3 can report you the battery wear level. Or you can install this app to find out how battery the battery is.
Iphone 6 with 64GB should cost you about HK$1500. At these prices I am not sure there is a point in buying Android Xiaomi devices... unless you can root them and install Sailfish for the security conscious user.
I might add that most repairs on iPhones are dirt cheap in Sham shui po now a days. Droppign and smashing it up is not something you should be too worried about...