from my calculation, cerato k3 1.6 new net selling price will be about rm93000 after gst compared to about rm96000 before gst..is it true? since the custom will return back the 10% of already paid sales tax and charge back 6% of gst..right?

that is normal..most probably because your car is stopped on the gearbox parking pawl..to prevent this u can try pulling the hand brake fully tight to prevent the car rolling backward/forward and stopped on the gearbox parking pawl..