I get my iPhone and put a silicone case on it and now and then clean it, I don't go over it with a micrometer, or a jewellers loupe, or an electron microscope! If it looks good to the eye then its fine.
These are mass made units from china or India or Vietnam and no matter where they are made, they are not a single unique creation you paid millions for. Also the more you swap the more you may get some realy bad issues and you also get noticed by Apple for wasting lots of their phones or other gear.
I remember some guy a few years back returned 16 phones I think, that's crazy, don't obsess, and the old 'I paid blah for this so it should be perfect' is bull, I paid a lot for a Sony master series OLED with 3 dead pixles at the edge of the screen that I cannot see unless I am like two inches away (or getting my cat down off the unit which is when I saw them about 2 inches away from the screen) now out of 8 million that's not bad, and the next unit could have much worse issues. Nothing is perfect no matter how much you pay, let alone mass produced phones tablets and TV's and computers with an Apple logo. Jeez get a life people.