I've been asked at traffic stops at least 3x, by police:
> You don't have any drugs in here, right? Don't mind if I take a look?
What do you say?
> Nope, no drugs!
Great, you've consented to a search.
> No, officer, I don't consent to a search of my vehicle.
They might still search, but now their search is without probable cause _and_ your consent, which means even if they _do_ find drugs in your car, your lawyer will be able to spring you easily.
Cops do take advantage of those who cannot afford lawyers, but a way you can set yourself up for success is guide the interaction in such a way that a lawyer would have no problem proving the cops violated their own guidelines.