No. You can refuse the police permission to conduct a search. Remember this -
the only reason the police officer wants to perform a search is for evidence of
criminal activity, and the fact that he is asking reflects an expectation that he
will find some. You are entitled to say "No." If the police officer has the legal
authority to perform the search, he will do so whether or not you agree.
However, if he does not have the legal authority to perform a search, your
consent gives him that authority.
During an investigative stop, or a traffic stop, a police officer may ask if he can
search you or your car. However, if you give the police officer permission, he
can perform the search even if he otherwise had no legal authority to do so.
Some people don't know, or forget, that they have an "open" bottle of liquor in
the car - a bottle with the seal broken, whether or not the cap is off.
Sometimes, people have knives or other weapons which can be classified as
illegal "concealed weapons." Sometimes, people forget that they have
contraband in their cars, such as illegal drugs, or find out the hard way that
their teenaged child dropped a marijuana cigarette in the car. Unless you are
the only person with access to the interior of your car, you may be in for a
surprise if you grant permission for a search. SIMPLY SAY "NO".