"As you add scale, your incremental cost goes to zero, " says Robert Greifeld, 51, a former computer salesman who took over at Nasdaq in 2003 as it was being spun out of the old National Association of Securities Dealers, now the Financial Industry Regulatory Authority.

FORBES: About Robert Greifeld

Here are some tricks and traps to be alert to, courtesy of Gerri Walsh, vice president of investor education at the Financial Industry Regulatory Authority (Finra), the securities industry's self-regulatory body.

WSJ: Why You Should Read What Your Broker Sends You