Seems like an isolated case where the buyer was really stupid. Although, it may help to know how any state laws might apply in this situation as I believe they do vary...
But if the seller did knowingly lead them into believing they house was worth 5X what they paid, I'd think there could be room for some potential fraud, even if the buyer was a dope.
Difficult to tell not knowing the entire situation or being a legal expert
-spence