One of the ERS units came out of the box with a pretty noticeable dent at the top left on the stainless steel band. There were also micro scratches along the bottom band. I thought Apple replaces the outside components that users touch? There's no way that someone doesn't notice that type of thing, since the dent caught light
pretty significantly.
As far as the other units, I only saw the back when opening the phone and front when I turned on the display to compare. I didn't look too closely at earpiece gaps at the top, scratches in the frame or cameras, flush SIM tray, etc. but nothing really stood out to me in all the phones I have tried.