Dealer convinced us that their "Ex-Demo" IRL "Ex-courtesy" car (the free car you get when your car is in for a service) was still classified as a new car, but was $20k off because it had never been purchased and had 10k on the clock... Lucky i checked the paperwork because it only had three days rego (SERIOUSLY!!!) When I brought it up, the guy went to the manager and reluctantly bought three months rego for it...
A month later we got a letter - turns out we got slogged for stamp duty because they told the RTA it was sold as a used car. Complained to the dealer and they tried to offer me one of their special "loans" to pay for the stamp duty. Sent a complaint to the ACCC and they said that they know about this kind of situation and there "is nothing we can do" because the dealers are very good at dodging the paperwork so they seem legit but technically the law is in their favour.
Stamp duty is payable on new and secondhand cars so I don't understand your gripe