Some shoppers now see a USPS doorstep-pickup as an Amazon return option—schedule a free pickup, print a label, box it, and USPS grabs it Amazon’s label-free, box-free drop-offs (Whole Foods, UPS Store ...
USPS is far from perfect. There are plenty of legit addresses that USPS doesn't recognize. College dorms, new homes or developments, old houses that have been converted to apartments, rural areas, etc. Often when USPS says they don't recognize an address, I put it into Google and come up with a photo of the house or apartment. In that case, I ship.
Why does Etsy allow buyers to put in addresses USPS doesn't recognize
Unfortunately, I have not been able to find a USPS Web site which states this clearly, and so for the moment will refer to this Web page by another source (which has links to USPS Web pages which are no longer active ).
@FrameTowne Did you choose USPS retail rates in one shop and commercial rates in the other shop? That would explain the difference. The $13.98 also sounds like it might be Flat Rate or Regional Rate shipping, rather than Priority by weight. In that case, it could be that your Package Preferences are different in the shops.