Unfortunately, the area that they were all meeting is not known for being a "nice" area. That's not to say that the assailant wasn't from some other city, though.
But yah, I appreciate your concern! I don't really sell things at all, and if I do, I prefer to do it online where there's some fraud protection and my interaction with the other person is limited. I'm paranoid even when I advertise empty packing boxes on CL.