"The law works on the basis of freedom of contract and caveat emptor, so, in these cases, unless there has been misrepresentation or unless it can be shown that the banks have taken on a special duty of care because of a fiduciary relationship (which most bank documents expressly exclude) the buyer is supposed to know what he is buying and the risks thereof."
Clearly, the relationship manager did mis-represent the product that they sold to the investors, who were generally risk averse. The question is, "did the RM understand the product?" Most likely, they did not. If this were the case, surely, they must have mis-represented the product?
The strategy for the investor is to provide clear proof that there was mis-representation. This can be in a sworn statement. Better still, it should be supported by an impartial witness or written documentation.