A lot of tourists get robbed by dealers in NZ, you've got to be careful... I was talking to a guy a while ago who got sold a car with faulty brakes. The dealer then tried to sting him for the repair bill and took his car off him three weeks while it was being fixed. This is actually illegal if the person that sold you your car is LMVD (licensed motor vehicle dealer)....
It's not exactly clear from your post what the relationship between Rodney and Canterbury Rides is. Is Rodney the place where you bought the bike or the man you bought the bike from? Is he a recognized employee of Canterbury Rides?
Under NZ consumer protection law a registered motor vehicle dealer cannot sell you a dud bike. But if you bought the bike from a private individual you don't have any rights at all. Is the man Rodney or the place Rodney a registered motor vehicle dealer? If so you can make a complaint.
Do some homework on the complaints procedure here
You need to be more clear about exactly what happened and when though. Construct your argument clearly and specificity dates and amounts etc. I know you're upset but your post reads like a bit of a rant and it's hard to follow exactly what happened, and which characters were involved.
Write a letter to BMW NZ about it too.
I'm really sorry that you had a bad experience in NZ. It upsets me that my fellow countrymen have ripped you off.
All the best. Let us know how you get on..
Jane and Mark - Russian Traverse 2007