Thanks so far for your feedback.
I offered an amended $11,400 post inspection, which the seller rejected and said he won't take anything less than 12K.
Haven't yet decided how to respond.
I am shopping for a car with evidence of IMS having been replaced, so that limits my search and rules out non-Porsche dealer trade ins, as none of the ones I checked out had any service history.
At this price range it also appears that some private-market cars are not necessarily being maintained well, so I'm not sure if I really can do better right now at 12K.
This car has also had the later top with glass window installed.
About the tires, they are all in good condition with a lot of tread, and I'm OK with being one size out. I don't intend to replace them. A taller sidewall is actually beneficial here in Ohio with typical road conditions....
There doesn't seem to be much on the market right now (mostly non-S, or high mileage, or no IMS evidence, or yellow/red which I don't want), and if I don't get a Boxster S in the next couple of weeks I will be buying my current BRZ at the end of its lease, and then who knows if I will ever get a Boxster, as I will probably just wait till Cayman prices go down a bit more before trading up...