I would definitely hold the dealer's feet to the fire if they misrepresented the goods (intentionally), but I'm not convinced that they weren't steered into believing that the goods were made in the USA to begin with.
How do you know they weren't misled? And, what degree of due diligence is required on their part? Do they need to contact importers if they had no reason to believe importers were involved?
If Tony Bose told me a knife I had on order was made in his shop in IN, should I have been sitting outside his home conducting surveillance to see if evidence of his making knives was present? Or would his word and reputation be enough?