An agent doesn't cost you anything and they are an advocate for you if something goes wrong. Some swear by using a Carnival PVP (which you will get if you book on-line with Carnival). Just remember that a PVP is a Carnival employee. All I can say is I've always used an agent for my cruises. Any prices you can get on-line are "supposed" to be available to an agent, hence the pricing you've found being the same.