<p><pre><code>  You&#x27;re right, for paper tickets there needs to
  be a trusted  third party that handles them
</code></pre>
Stubhub does no such thing.  For physical tickets, seller ships to buyer.  For PDF tickets, seller just uploads them; the upload constitutes delivery.<p>For events that Stubhub lacks hooks into the ticketing system (mostly baseball), they do nothing to vet tickets.  Buyers are advised to create a listing in TicketExchange (or whomever <i>is</i> the official marketplace) to (1) validate the tickets and (2) lock them to prevent forwarding or TicketExchange sale by a prior holder.