In a world where disclosure of information is at the touch of the fingertip I think its prudent for buyers to do their due diligence, now that being said , I think its fine for a business to recoup losses I also agree that it would be a huge loss of said resources and I believe VW could purchase the green credits as an off set to the co2 increase...
If the potential harm was only going to fall on the owner then I think you are right. Buyer beware.
In this case, though, the harm is to the air-breathing residents of the buyer's city. That has to change the moral problem, doesn't it?