First, how do you know your friends got the same itinerary for half the price? I'm not saying they are lying, it's just that hyperbole can get the better of us sometimes. And remember a published fare is not the same as an available fare.

Published fares, those available to the general public, are out there for all to see, to both agents and individual travelers. So generally when you are looking at availability at any given time within the same time period, I should not think there would be be a great deal of difference between sites- certainly not by half.

Travel agencies often use unpublished or consolidator fares that are negotiated rates cheaper than published fares. But these come with restrictions-- less to no FF accrual, etc. These are mostly for international travel.

As for finding an agent, recommendations and using one enough that you become a recognized client can help. But there can be a lot of turn over. Just as soon as you find one you like, they leave.

Ask around. That's the first step.