The volume of transactions on eBay makes it difficult for police to prosecute specific cases for a variety of reasons, but the most common is manpower and the issue of jurisdiction. However, when police have a well-publicized instance a crime occurring in a specific area with already known suspects (in your case, the police would have needed to attempt to find the person whose phone was lost before proceeding) with key details being admitted by the suspect prior to the involvement of police, then you can damn well bet that there's going to be action. To think otherwise is simply naive.