Perhaps it means that you can't dictate the value of an instrument to somebody else. Everyone makes his own assessment of an item, so if someone wants to buy it from you above what you think it's worth, or conversely, sell it to you below what you think it's worth, it's your freedom to trade and not your business to try to change his mind.

However, persuading a potential buyer that something is worth a high value while secretly you believe the value is low is another matter. That's what people do all the time, though, not just bankers. For example, a lot of sales people do that.

However, there is a difference. Most people know to take what a sales person says with a grain of salt. Besides, if you don't like the sales person or his product, you can always walk away. In the case of banks, there is a lack of integrity somewhere. People were expecting the government to protected their interest by making and enforcing the right regulations. The government didn't do that and banks made off with public money. The government involved the public in its complicated legal and financial system that is hard to understand for common people, and failed to make it work for them.