What's the difference between Wall St banks and car salesmen?

Nobody expects someone selling them a used car to point out all of its flaws. And if you believe the salesperson who tells you that those pants look absolutely fabulous on you, you either have amazing self-esteem, or you're deluding yourself about what people will do to earn a commission.

So why should we expect Wall Street financial institutions to be any more trustworthy than the lemon-hawker down the street?