151389560917 is the eBay listing number. ReferenceID is an eBay internal number representing a product similar to a UPC code. The API calls return the ReferenceID when available. Use findItemsAdvanced or GetSingleItem or GetMultipleItems to retrieve the RefID, then pass that to the product lookup to get useful info like UPC code. Your item does not appear to have one. They're only available on items listed from the catalog, which generally means products with a UPC/EAN (try item 331351986423), but may include addl items. Life would be so much easier if eBay just included UPC/EAN code in the response along with ReferenceID
Thanks for your answer. If I want to invoke GetSingleItem from Java, is there some convenient mechanism for that (like there is for FindItemsByProduct) ? Or do I have to submit a web service call and then parse the resulting XML?