In the Porsche factory used car lot cars go for ABOVE retail. Why?
Each engine that is build is dyno tested and must make between 100 and 105% of rated power.
If it makes less than 100% it is rejected and the person who built it has to determine why and charge back the appropriate vendor or log a build mistake.
If it makes more than 105% of rated power it goes into an executive car, to be driven by a Porsche Exec for a period of 6 months. It is then returned to the factory and sold as used.
Buyers know this and are willing to pay a premium for these cars.