The shipping calculator on the eBay.com site relies on a shipping calculator API that is not owned by eBay. This 3rd party shipping calculator does not always support the full set of features that are available directly from UPS and USPS.
A known limitation of the shipping calculator on the eBay site with respect to UPS services is the 150 lb limit on the Dimensional Weight of an item. The shipping cost calculation service on the UPS.com site supports a higher limit on the dimensional weight than the service used by the eBay site.
The dimensional weight calculation for an item listed through the API is as follows:
PackageWidth x PackageLength x PackageDepth / 194 where the dimensions are in inches and the result should be rounded up.
If the result of this calculation is greater than 150, then the shipping calculator on eBay.com will not be able to calculate the shipping cost for the item. This limitation will not stop the item from being listed, meaning that the AddItem call will not return an error or a warning.
The ViewItem page will simply show the following message:
"Shipping cannot be calculated for your area. You can contact the seller for additional shipping costs and services."
The Review Your Purchase page in the checkout flow will not show the UPS shipping service calculated costs.
There can be other specific instances when the shipping calculator cannot make a calculation.
If a bug is suspected with the shipping calculator, and no explanation or resolution can be given by eBay.com customer service for shipping calculator issues, you can always file a Support Request.
Please be sure to provide the complete details in the support request in order for us to provide you the best service possible.