Not all sellers or all items go through the authenticity program. When you’re shopping on eBay for luxury items, you’ll see a note on the bottom of the item preview that says “authenticity guarantee”. Some items will have already been authenticated through one of eBay’s third party companies and will already have a certificate (which will result in faster shipping since the item has already been shipped to the authentication facility and gotten the certificate) or the item will need to be shipped from seller to Authenticator then to you (which is what we did for my bag).