People will let you search their cars KNOWING full well what's in there will ruin their lives...and I can't explain it either, but it takes little more than asking in the right way in most cases.
Yeah,... well,... if ya say "no", they bring this mean ass dog in and let him sniff around on ya car, and if he runs at ya and starts eatin' on ya leg afterwards they call it probable cause and search it anyway.
So,.... you got two choices. Let the cops search ya car while ya gettin' et on by a dog,... or let 'em search ya car while ya just stand there.