Legendary Journeys recently ran an ad in the Sun for a cruise to Australia and New Zealand for an outstanding bargain price. Upon calling the office it seemed that all of the slots at the super good price were gone. (Bait and switch?)
Further, if you actually wanted to go to New Zealand that was for an add-on cost, not included in the advertised price which seemed to indicate that both destinations were for the great price.
I have successfully used AAA Travel for booking of most of my cruises over the years although I still go directly to the various cruise line web sites to price shop before making a reservation.
Cruise Critic web site is also an excellent place to comparison shop. There is also a message board where travelers exchange information about their experiences with various lines and specific trips.