Wow, 11 phones, that must be pretty insane, especially since it seems that there are numerous others that have been through similar amouts of phones. If you can, I suggest you maybe take it back and return it for now. The scratches may not be too much and on my phone, I convinced myself that I would overlook them. However after thinking about them more and the fact that if they do fix this, I would end up with a damaged phone while in a few months, others would have be using perfect ones. I decided that I should just try fix the problem now instead of feeling regretful later on.
From what it seems like, AppleCare through the phone are providing better service than in stores.
I bet if a company can make a process of polishing or what not to fix the scuffs on iPhone 5s, they would make a lot of money right now!