What vi_edit said. Been burned by that myself.
The AGENT represents the seller, and has a contractual obligation to act in the best interest of the sellers (ie, get the highest price).
A BUYER BROKER represents the buyer, and has a contractual obligation to act for the buyer. If you get one, you must sign a contract, and you must work through the broker in order to see any property. Do NOT have an AGENT show you a house w/o checking w/ your broker.
Sales Commission is usually 6%, and is paid by the SELLER (so it's built into the price of the house). The commission is traditionally split 3% to selling AGENT, and 3% to the BUYER BROKER or agent who brought the customer to the house. Note: A buyer broker defines a very specific legal relationship, and is not the same as working through a particular agent.
What the RE folks recommend, is that you work through a single AGENT, who will work with you to identify properties that might be of interest to you. The properties may be listed by the same agency, or a different one as the one you are working through. "Your" AGENT will get the 3% commission on any property you buy, that they showed you. This is why you have to be very careful about who shows you the property! Obviously, if "your" AGENT sells you a property that is being listed by their own agency, the agency gets the whole 6%. Be aware, even if the "your" agent is not from the listing agency, they have more of a responsibility to the seller, rather than to you.