Originally Posted by
40love
we searched CGK-AKL and air NZ ran this as CGK-DPS-AKL
As per above comments, it has been explained why it can be cheaper than DPS-AKL
are you saying we could stopover in DPS like your son stopped over for 3 weeks in BKK? Because I couldn’t see any option to stay 3 weeks in DPS?
As hinted at above. You need to try build what you want to achieve. If the online multi-city tool cannot cope, then a decent TA probably can. But it depends on digging deep if it gets tricky, and there can be annoying fare rules; for example some fare levels require a minimum number of nights at the 'destination' and/or have limitations on a 'stopover'.
The digging around yourself is (IMHO) vital to learning what is possible and how to achieve it
40love edited to add - see the example booking quickly constructed on the AirNZ site.
Note that this is $80 more expensive than a simple AKL-DPS-AKL, but hopefully this gives an example relevant to the general point.