As someone who notices gaps, clicks and all tiny cosmetic imperfections, I'd sell this phone at a loss on ebay or facebook marketplace.
I did an "apple store hike" with iPhone 6 back in the day. Sim card slots were not flush with a lot of units. And then with 6s - screen brightness wasn't uniform, darker at the bottom. Likely because of introduction of 3D touch. Almost all units were like these. Out of 60+ 6s iphones I've seen, only one was "perfect".
With 13 pro it could be multiple batches with gaps like these. It could be one large batch. In both cases finding "the perfect one" would be tough.
If it's a minor thing like this, and Apple will consider it minor, in my opinion (like sim cards and screens with 6 and 6s), they usually fix it in the next gen.