Correct. The police do not exist to clear you of crimes. They exist to arrest you, guilty or innocent. NEVER SPEAK TO A COP, EVER, ABOUT ANYTHING. Get an attorney to do all your talking for you.
Solid advice.
Although I've never been an officer, I come from a family of police officers (father; mother; brother; nephews). Without exception, all of them advised that throughout a traffic stop, especially if asked to consent to a search of your vehicle which you must refuse, do so politely and calmly (despite any inner turmoil). Then be sure to ask -- politely -- if you are free to go and, if not, if you are being detained. Some officers may get "huffy", but maintain your composure, be polite and you'll do just fine almost always.