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Six car dealers have been fined and told to clean up their act, after a Commerce Commission swoop.

They have been fined a total of almost $11,000 for not showing the right information on Supplier Information Notices, or SIN cards, on used cars.

The Commerce Commission says it is a must for used car dealers to display them, so buyers can shop around and compare.

The companies caught out were Kobes Cars in Levin, Stuart Cheyne Auto in Napier, Marple Investments and John Dudley Motors in Wellington, McKenzie Motors in Masterton and Sunrise Motor Group in Porirua.