I state in my ad that I will only respond by phone, so the responder must include a phone number. I also always include my phone when I respond to an ad. I got a $10 TV last week and it helped to actually just talk by phone, hash out the details, get directions, and be done with it.
I am lucky in that we have daily classified ads where I work, so I'm able to sell most of my stuff to co-workers. However, every now and then, I use CL. I typically meet people at the grocery store when I sell stuff because I live so far from a town. That seems to work well. Most of the stuff I have sold is baby stuff, so moms prefer being able to meet at a parking lot, car to car, so they don't have to take out their baby. I think everyone feels safer that way too.