I haven't had many problems, just minor stuff. Got to use street sense and common sense. Don't buy a $2000 bike off CL, Duh????? Get robbed, riped off, bike is a fake, many scams. But I bought my bike ( and many other things) off CL and it was cool.
Never place yourself in harms way.
Try to meet at a public place.
Always take a friend or let someone know your whereabouts, plus whatever description you have of the other person.
In seattle, I like to meet in front of the County Sheriffs office...