CL requires a certain degree of caution. I've never sold a car on there, but I know it is done quite frequently. I've mostly sold odds and ends. When I make sales, I do it on neutral ground in a very public place, such as a parking lot at a busy grocery store or something. I only make sales in cash (and I even have a marker to check if the bills are legit). Never, ever use checks, money orders (unless they go with you to redeem them), wire transfers of any sort, etc.
In your case, it might be a good idea to bring a friend along to witness the sale and test drive. For the test drive, I don't see a problem with trading their ID for the car temporarily so they can drive it around a bit. If they try to steal it, they'll easily be caught. If you ride along, bring your friend. I highly doubt you'd be at risk of kidnapping in that situation.