How to check if the screen replacement part for iPhone 5s is an original one?
In all likelihood the screen won't be original. You'll be able to tell from a number of factors but none of them are conclusive as fake screens can exhibit any of these indicators...


The glass should be a deep black or neutral white, not grey, or cream.
The phone shouldn't feel heavier, often fake screens are much heavier.
The grille over the ear piece should have a fine black mesh not silver or with large holes, or missing.
After cleaning the screen, if you place the screen in a bright pin/spot light you should see a streaks of rainbow colours in a criss-crosssing diamond pattern.







The thickness should be the same as before, fake screens are often almost twice as thick as originals.





You shouldn't be able to see the proximity sensor in the glass, and if you can it should be a neutral grey not a blue transparent look.