Yes, we booked through AAA once, but when we wanted to book NCL our AAA TA wouldn't do it! She said we wouldn't like
NCL. (I'd done my "homework" on here and thought we would.) Later I found that NCL wasn't paying as much commission as other lines.
We found another (wonderful!) TA who was more than happy to book our cruise, after finding out that we knew what we were booking.
I'd check with AAA, a "brick and mortar" TA, an (any recommended on CM's) online TA, and the cruiseline directly before I'd make a decision.
This seems like a lot of work, but it will pay off
Yes, on any cruiseline (as far as I know) if the price of the cruise goes down before
final payment you can get the lower price. You may find a TA who will offer some OBC or some other incentives, but this doesn't count