You can contact
order@yubico.com if you wish to initiate a return. I've seen scratches on plenty of new YubiKeys in the button area. The area to be concerned about is the USB contact area. You'll see scuffing on the contact area after only a few removals and insertions. The damage in both cases is in the outer oxidation layer and nothing to worry about (from a functionality standpoint). For piece of mind there are also several checks you can run to see if any changes have been made:
- Personalization Tool should show only slot 1 is configured
- test at demo.yubico.com with an identity beginning with "cccccc" should pass (if both things happen, the identity is original)
- do a test registration at demo.yubico.com/u2f
- if you have gpg installed, gpg --card-status should show no identities loaded
- running YubiKey PIV Manager should bring up an initialization dialogue and allow you to set a PIN
- Yubico Authenticator can be run to ensure no identities are stored (should say "no credentials available")