You're right. It isn't risky. It's just that I would only take cash for something on CL. Why would somebody rob you when you go to buy his truck? You know where he lives and you know what he drives. He would have to be insane to try and take your money.
Until you learn that he found out Joe Schmidt was on a vacation trip for three weeks, the same Joe whose house isn't very visible from the road and neighbors. He took photos of Joe's (second) car in his driveway, and posted it for sale on CL. Then made the appointment for the CL buyer --perhaps YOU?-- to meet him "at (Joe's) home" to complete the sale.
He went there a little early, broke in through a back laundry-room or basement window, found the car's registration papers in Joe's desk, and when you visited, completed the sale, letting you think all the time that he was Joe. He made sure no pics of Joe were hanging on the wall where you might see him, and basically the whole transaction took place outside by the car, anyway. [Just in case, he had already made sure he knew where the bathroom and kitchen were, in case you needed to use the former, or were thirsty.]
By the time anyone realizes the signature was a fake and this stranger sold a car that wasn't his, he's long gone from the property, and the only evidence anyone has is your hazy memory of what "Joe" looked like. You paid cash, and you aren't getting it back. The owner has reported the car stolen, the court determines that the sale document was fraudulent, and returns his car to him. You're stuck, unless they catch the criminal and manage to get the money back from him...both of which are very unlikely, if the criminal is smart.
This scenario, which requires only enough chutzpah on the part of the crook, can't happen with a PayPal payment.
Of course, you should always ask for photo ID before completing any such transaction, and ideally get a copy of that ID. If he's smart, he'll have photo ID ready --although most guy's won't bother to go that far-- and won't let you copy it, because of security and (he says) identity-theft fears.
If someone really wants to cheat you, you need to be very on-your-toes to prevent it. Fortunately, most criminals don't want to work that hard (Otherwise, they'd get real jobs and earn the money legitimately?), so they'll try things like that CL listing, and look for the easier suckers to cheat, instead. The same way they'll look for harder houses to Rob than Joe's neighbor's house, which has security alarms, CC TV recording with remote monitoring, etc... Ultimately, avoiding becoming a victim of conmen and criminals is mostly about common sense and a little precaution and vigilance.
I feel sorry for anyone taken in by something like that CL ad, but I also think such a victim is very foolish/naive.