I have to wonder if the seller really was intentionally deceptive or not. Anyone who buys or sells a lot of Japanese games knows what a Seal King bag is. He would be "found out" as soon as the buyer had the item, so why bother lying about it?
It seems more likely he just doesn't know WTF is going on, took a glance at the plastic, and thought that it was the original plastic. He should be educated about this and then he should refund some money.
This, BTW, is exactly the sort of stupid shit that will always happen to collectors of sealed games. Its a stupid scene, and I'd suggest avoiding it. If you don't like actually playing games, don't by them.