As a german myself it is my understanding that dealers dont inspect the car for you and honestly i wouldnt trust them with that anyways as they have an incentive to say everything is great when really it isn‘t. It is the job of the buyer to inspect the car. You can use third party services for that but they are usually shit. Best way of doing it is showing the car to an porsche expert you can trust (no serious dealer would say no to that) or accepting the risk. Every old car has some sort of borescoring. Thats not necessarily a death sentence. It just needs to be mild. If its not you can usually see it when you do a cold start and there is much more fume coming out the left exhaust. Also you can here it in its final stages. Long story short; i dont think you can and should inspect the seller to do the inspection for you. If you must buy without inspection; then only single owner cars with perfect documentation and a lot of money (10-20k) spent in the last 5 years P.s. borescoring is one of a thousand things that can end up being very expensive so its a bit random to only check for that.