Interesting how people have various experiences with private sales, mine go like this:
350z - Sold to the first viewer, no haggling or trouble, he transferred the cash and waited a couple of days for it to clear done.
M3 - Sold to the first viewer, had a few timewasting calls and a lot of 'Part Exchange' emails for some shitbox or another, ended up selling for less than I wanted to, but for £4,000 over the nearest P/X
S4 - Sold to the first genuine enquiry, who accomodated me in a crazy situation. Basically he called on Friday night and on the Saturday I was heading to London to collect my 335d. As he was in London, we agreed to meet and he pay cash, on the proviso that he then drop me at Baron's Farnbrough. I met them, he liked the car, we went from bank to bank closing his ISA's and as promised I arrived at Baron's with a £13,500 in cash in my pocket. I got £1000 more than the PX offer and I also paid £1000 less to Baron's because we'd agreed a cash deal was better for them - they didn't want the S4.
335d - I sold the 335d privately for cash 18 months and 30,000 miles after I bought it for a £3,000 loss over what I paid - good business. The bloke paid with a carrier bag full of cash which was all legit. I had a lot of nonsense PX emails for this before it sold, but I just ignored them or told them no.
135i - I sold the 135 privately to a guy through Pistonheads. He was the first viewer and paid by instant transfer then drove the car away the same day. It took a few days to sort out but was no real problem. Again I had a few PX emails but nothing too excessive.
Boxster S - This didn't sell privately after a month or two up for sale. Eventually a broker contacted me and saw the sale through for me - hence I lost a grand to him, but I also got a grand more than the kind of offers I had when it was up for sale privately. Does this count as a bad experience? I don't think so.
Golf GTI - Eventually sold privately here and I think both me and the buyer are happy - including mods, I lost just over £8,000 on that car but that is cars for you. Before that, I had a number of emails with stupid PX offers and so on, but no crazy price offers, no tyrekickers and no 'in the flesh' timewasters. One bloke did view and 'not buy' but he wasn't a timewaster as such I don't think.
So that's my experience basically. I'll always sell privately if I can until something tells me it's a bad idea - so far I've met some great people. If you find timewasters are a problem, tell them to fuck off on the phone before they even view the car!!