Just being respectable will not get you off the hook 100% of the time, it's roll of the dice. It certainly doesn't help the situation if someone is acting like a prick towards the cops though
I was a passenger in a mates Supra once, stock on the outside beside an exhaust & wheels, got pulled over in an RBT. Police asked him open his bonnet, my friend was co-operative & polite the entire time but still got ordered to an inspection station for exhaust & pod filter