I'm so sorry this happened. You really can't be too careful when meeting people you don't know. I went to pick up a free tank from a Craigslist ad and I wasn't able to get anyone to come with me during the time window specified. I still went (alone), but I gave the address to my significant other and we worked out a plan that I would call when I got there and that I would check in again within 30 minutes. If I didn't check in, he would call my cell. If I didn't answer, he would call the police. Sounds crazy-paranoid... until you see a story like this one.
As expected, the person with the tanks couldn't have been nicer and nothing suspicious happened whatsoever. He had even brought the tanks outside so I didn't have to go into his house. 99% of the time, everything is fine. You just gotta be prepared for the 1%.
So right Cello. It is sad. My sister and brother-in-law are constantly running ads to sell stuff like cars and rugs that they purchase and then decide they want a change so they sell the items on CL. They have strangers entering their home to look at the stuff and sometimes my sister is home alone with the kids when people look at stuff. It drives me nuts--I tell them it is not a good idea because of that one person who is the bad apple. They don't listen though.
It can happen on Craigslist, any other online classifieds, your local newspaper, a garage sale, a parking lot, your own back yard...etc
Face it, this world is FULL of demented people and you have to be careful no matter what you do.