ferrari dealer for service/inspection or independent?

In my opinion a PPI (post purchase investigation) could happen by either an independant mechanic or authorized dealer as long as they aren't linked in any way to the car.(know the seller or conducted service on the car before) In that way they can perform a subjective investigation on the car.

any dealer as long as it has a good reputation and good experience with the car.

As I have often mentioned before, Ferrari from the F355 onwards need a dedicated computer to do a complete diagnostic check for maintainance and repair. So it is obvious then that late model Ferraris have to go back to the dealer for this. If it's just a matter of visual inspection to see if the car has been involved in n accident then any mechanics can do that. But if you're going to spend US100,000+ for your Ferrrari, why stinge on the official dealer check-up?

That is why I said they got to have experience with the car. I they can't work on it they can't do a good PPI

Answer does depend on the age of the car: for early/vintage models you almost have to go to a qualified specialist as most of the official dealer's mechanics have little to no experience with these models. For later cars (F355/456 GT onwards) you need either an official dealer or a specialist with the right diagnostic equipment. I have had both positive and negative experiences with both.