Registration and identity
Zulassungsbescheinigung Teil I and II must match the chassis number stamped in the car. Any mismatch, overstamp or replacement plate needs a documented explanation before money moves.
History and expenditure
Service books, invoices and photographs of past work show how the car was kept. A thin file is not automatically a bad car, but it should be reflected in the price.
Export and customs
For a car leaving the EU you will need the export declaration, invoice, and often a certificate of conformity or age certificate for the destination country's registration authority.