What happens is that the figures are all uploaded to State Revenue... if yours sticks out they will investigate and give you a minor fine if you can't prove it.
With mine, there was such a myriad of paperwork inc. FOB charges, duty, shipping and all that, they just gave up and accepted my figure.
They're not interested in chasing up little people like us.
If you import a 1961 Ferrari and say it's $50,000 rather than $250,000 well then yes, they'll f**k you over.
However a $10,000 R33 that is more likely $15,000??? No point.
T.