Autotrader is rubbish. Their searches ALWAYS show trade cars first and they are ALWAYS misleading so from a private sellers POV I would not give them my money.
Ebay is ok but you do get spam emails from Nigerian businessmen asking to buy your car for asking price if you'll pay for a courior to deliver it! WATCH OUT they can be quite convincing.
I had one woman actually go through the Buy it now process and upon paying for it, she 'realised' it was an older model to the one she thought even though my description and pictures clearly showed what it was!
To avoid the above problems, advertise locally. Newspapers, Loot etc are worth using sometimes (depending on where you live).