The cruise lines now have very strict policies forbidding travel agents from offering discounts or perks out of their commissions. Thus, your travel local "brick & mortar" travel agency should quote exactly the same fares as the company's web site and all Internet agencies unless one or another is forming a group.
Norm.. that's not quite true. On some lines the price has to be the same, but the agents are allowed to purchase "perks" (from the cruise line) to offer to their clients... such as an onboard credit.
Agencies are allowed to offer other perks.. such as free insurance, or a pre-cruise hotel stay,etc.
And there are normally plenty of agencies offering group rates.
So... it still pays to shop.