The last time I tried to sell a car privately was 15 years ago. Since then I have always traded-in my cars (at considerable loss compared to private sale, as you would expect).
I still remember some of the calls I received at the time. The car was advertised at £9,800. One caller asked me first thing if the price is negotiable, I said that if by negotiable he meant reduce it by a couple hundred quid, then if he really wanted the car and wished to go ahead with the purchase, I might consider, but otherwise, no, the price was negotiable. He kept me on the phone asking various details (the car was immaculate, main dealer serviced, and being just two years old still had the remains of the manufacturer's warranty). At the end of the conversation he asked me if I would take £,6000 for it, and when I said no, he hung up and never called again.
Another caller asked the usual questions, plus some odd ones that were very difficult to answer... one such question was - upon learning that the car had standard (non-alloy) wheels - 'why does it not have alloy wheels?'. How do you even begin to answer that? There were more questions of this kind.
That was in the good old days of Autoloader and Loot... I can only imagine the depths of silliness some buyers can reach now that we have eBay.
I don't blame the seller of the SL500 for the wording in his ad.