When I do a flat rate shipping, it's because I haven't boxed up and weighed the item yet. Since he put in his listing that there might be an additional fee to the East Coast, and since the additional fee is $5 and not something higher, I would mark it off as unusual but not intended as a scam. I don't think it's worth hurting him or his business over this, although I agree that someone will eventually respond with negative feedback or escalation etc.