Do stockbrokers work for you or against you? The answer might surprise you.

Under what's informally called "the Merrill Lynch rule," stockbrokers are allowed to work against the best interest of their customers. By contrast, an independent fee-only financial planner who does not work for a brokerage firm has what's called "fiduciary duty." That simply means they must do what's best for you.

Surprisingly, many investors are very misinformed on this point.

A couple of years ago, The Wall Street Journal's Jason Zweig cited a study that found roughly two-thirds of investors -- we're not talking about the general public here; we're talking about dedicated investors -- thought stockbrokers had to work for them.

If you do business with a stockbroker, you do so at your own risk. If a broker wants to put you into a bond fund, that broker can legally look for the most expensive option to your great harm.

But don't take my word for it. The ReformedBroker.com is a blog written by a former full-commission guy who when out on his own. As he says, "I realized that most of what I did was bad for clients -- so I quit.' His blog betrays the dirty secrets of full-commission stock brokerages.

Of course, some individual stockbrokers rise above this corruption and conflict to defy their brokerage house by doing what's in your best interest. However, I believe they're few and far between.

So be sure you know what most active investors don't -- that stockbrokers help themselves first and you second.