Halbe, 21, from Olpe near Cologne, bought the car from a private dealer for over £6,000 just six months before Pope Benedict took the helm in Vatican.
They would be investigating the last few hours where there were "proven bidders who wanted to offer more but whose bids for higher amounts for unknown reasons were not registered on the eBay site".
Lawyer Juergen Langer from the firm has called on eBay to explain the problems. eBay in Germany admitted the car had been the most popular item ever to have been sold on its pages.