Case in Toronto, Canada a year or so ago. Two guys responding to a used truck ad. Then went on a test drive with the vehicles owner and killed him.

At least they were caught as well. It was absolutely premeditated and the truck would have been parted out.

If a neighbor had not observed the vehicle that dropped the two prospective purchasers off. I believe they would have in all probability pulled it off. They even owned a large animal incinerator. They have at least been tied to one more murder so far.

You cannot protect yourselves from all possibilities of harm. It is just a small risk factor in life that anyone can accidentally run into the path of a seriously sick sociopath.