Ya, I'd be sceptical about the mileage unless there was a paper trail from previous owners. There are still a few series II Interceptors out there. Some are restored and some are original. The ones with low mileage usually busted a con rod and sat in a corner for 30 years till someone finally came along and fixed them. At least you hope they fixed it!
It would cost a fellow much less to put his labor and funds into a good restorable bike than to buy one of unknown origin for $15,000.00. There are several RE twin models that are more rare and valuable than a stock series II. He might just get it though. There are plenty of impulsive buyers that frequent the bay.