I don't know if this would considered a scam or something more sinister but the guy was trying to scam me for something.
When I was 18, working my first job, I had a flat tire on the way to work. It was on a fairly busy highway, but at an off time, so while there were cars driving by, it wasn't just crazy or anything. Anyway, I was waiting for the person I had called to arrive and some old guy in a pick-up stopped. He came back to my car and told me he could fix my tire and get me back on the road. Great. Only one problem, he wanted me to get in his truck and run to his house with him to air the tire up because he didn't 'feel safe' leaving me on the side of a busy highway. I kept telling him no but he wouldn't leave. I was in my car with the windows up and the doors locked. This was pre-cell phone days, so it was either stay in the car and hope he didn't break the window or jump out and try to make it to the business a few yards away.
Thankfully a friend of my brother's came by and stopped in his tow truck. He had recognized the car from when my brother drove it. He got out and saw the man and me frantically motioning for him to leave. So he got a tire iron off the back of his truck and started towards the guy, yelling, asking him what he was doing. The man took off to his truck and sped off.
My brother's friend fixed my tire and followed on to my job in case the guy was just waiting further up the road.
I always wondered if I should have called the law or if the guy was really a nice but clueless old man. Better safe than sorry, though.