I own a Pin. I would not buy any carbon Pinarello from even a retail outlet unless I could trace its heritage and handling right back to Trevisio. That is, bill of sale, retailer invoice back to the (authorized) distributor and from the distributor back to the factory. That is all consistent paperwork that specifies exact frame specs and serial number on every document Even then, I would contact the factory diirect for confirmation.
Great frames, but I figure the chance of buying a (real) used Pinarello without this documentation is not even close to 50:50.