Find the answer to your question
Can I get the Seller Contact Details for an eBay Motors item if I have neither a transactional relationship nor bid for the item ?
You can get the information only if it is a Classified Ad format item and the Seller has listed it with the SellerContactDetails information. You can make a call to GetItem and if available, you will get the information back in the SellerContactDetails container. You cannot use the API call GetUserContactDetails to get the seller's contact information.
If GetItem does not return the information, you will need to use the link on the ViewItem page for the item to contact the seller.