In addition to bringing a mechanic, maybe you can check service records kung saan siya nagpapagawa.

Hindi mo din naman ma-conclude na friend mo may kasalanan kasi friend of a friend lang eh sobra na ang tiwala mo. For all you know, di naman alam nung may-ari na may sira yung car -- lalo kung de-driver. Try to strike a deal na lang. Kung may pagpapahalaga yung friend of a friend sa friendship ninyo, he'll compromise somewhere.

Pero talaga ngang certain things are 'standard' na dapat palitan pagkuha pa lang ng 2nd hand car. May thread nun dito somewhere. Just do a search.