Did exactly as I would.
Its not any different than someone going up on a porch here or around back of the house 'just looking' for trash. Sorry pal. When its out on the sidewalk with a 'free' sign on it, its all yours. When someone is looking around the property, they are acting like a potential thief. The last thing they ought to be doing is opening doors or the hood. Knock on the door is OK, but he shouldn't be surprised by your response. He would have done a lot better if he showed some interest in the situation rather than that his main interest was taking it. Some people think everything and everyone can be bought.