You, as a former TA, should understand the "back office" dealings that cruise lines offer to larger agencies (online and brick and mortar). Probably volume based. I also believe the cruise lines work with these humongous agencies to give them good pricing that no one else can touch and the agencies do NOT pass along the entire savings to the client.
In my experience, I've found that once the cruise get booked, the humongous TA's monitor the pricing the cruise line gives (watches for cruise line price drops), rebooks the voyage for their client at the new lower price and KEEPS 100% of the savings. The client never knows there has been a price drop they could/should have benefited from.
I'm aware of at least one small brick and mortar TA who does the same monitoring of cruise line pricing after getting the booking and gives the client 100% of that savings. Probably not considered "good business" as her commission goes down with the lower price. But, worth it in customer satisfaction.
I'm not a fan of the online, big box store, or humongous agencies … can you tell?