Six people have been fined a combined $32,250 in the last month for selling too many vehicles this year.
It is against the law to sell more than six vehicles in a 12-month period without being registered as a motor vehicle trader.
The unregistered traders sold 10 to 15 cars each from Invercargill to Waitakere in the past 12 months.
They were caught out by the registrar of motor vehicle traders at the Ministry of Business, Innovation and Employment (MBIE).
The harshest fine was $7500 handed out to a 42-year-old man for selling 12 vehicles without being registered.
Karla Flood, leader of the registry integrity and enforcement team at the Companies Office, said when buying a car it was safer to buy from a registered motor vehicle trader.
"With Christmas just around the corner, you may be considering purchasing a car as a present for a family member or loved one," Flood said.
"Make sure that you buy your vehicle from a registered motor vehicle trader.
"Unregistered motor vehicle traders are not subject to the checks that apply to those who are registered and consumers may have less protection when something goes wrong."
The registrar of motor vehicle traders worked with organisations such as Trade Me, Customs and the NZ Transport Agency to help identify unregistered traders.
The registrar's aim was to assist the traders to register so they were compliant with the legislation and only if this did not succeed did enforcement action take place.
Since July 2012, the registrar has investigated 358 unregistered motor vehicle traders. Of those, 279 investigations have been finalised, 61 remain under investigation with the view of achieving compliance and 9 cases are now before the courts.