Seems to me this issue is easily disposed of (of course, I may also be opening a most interesting can of worms...)
When it comes to knowledge, power, money, and the ethics of buyers and sellers, it seems to me that Kant's Categorical Imperative applies quite nicely, to wit: "act only on that maxim by which you can at the same time will that it should become a universal law."
A moment's consideration of the consequences of Kant's rule and I can't help reaching the inevitable conclusion that a seller has the obligation to disclose *everything* they know, or suspect, about what they're selling...and even more, the seller is obligated to *find out* things they don't know about what they're selling...regardless of price or circumstances...
Conversely, by the same rule, buyers should educate themselves about what they're buying, and ask the right questions...but, it does seem to me that Kant's rule lays more responsibility on the seller...\
Of course, American capitalism laughs at Kant's rule daily, if not hourly...
Charles "I tell everything I know and suspect. Customer satisfaction is more important to me than a buck or two" Andrews