[KevinP73]

Originally Posted by cstreit

My thought exactly, so refusing the search is grounds enough for the officer to search your car, because it's suspicious?

In a word YES
(In most cases) An officer has already determined/decided if he has cause to search your vehicle before he even makes contact with you. When he asks you if you will consent to a search he is simply stacking the deck (probable cause) in his favor by adding your reluctance to be searched the situation.