Bought a Boxster from a bum

[elgyqc]

I would carefully search all possible hiding places for unusual non automotive substances. Why would he want to buy back a car in such bad condition if his is homeless? Or maybe it was his home...
If you have the mechanical abilities and a place to work, start looking for a used engine.
Blow the fuel lines out with compressed air and see what comes out.
I'd try to start the engine after checking the oil.
Remove the carpets and clean them and let the interior dry out. Cleanup the surface rust and apply anti rust paint.