The problem is this can be more of a hassle for you. I've been pulled over as a teenager and when I said no he decided to search my car anyway. Saying no doesn't always help, in fact sometimes it makes them give you more trouble and search harder.

If you had consented to the search, then anything he found would have been admissible in court; By not giving your consent to the search you made it so anything that was found wouldn't have held up in court. A cop only asks to search your vehicle if he doesn't already have probable cause to do so without your permission.

> Saying no doesn't always help...

No, the police would like for you to think that. But imagine this scenario. You just dropped off a few friends. One may have dropped his prescription pain killer in between the seat cushions. Now, you've consented to the search and they found that dropped pill. You have no recourse, no prescription for a controlled substance and all you can say is it's not mine and you don't know how it got there.