Usability 
Looking to buy or sell a used car or motorcycle? If you are in the UK, AutoTrader looks like it would be helpful. It started as one of those free shopper magazines that you find on racks at the supermarket but has expanded to include a website and now a mobile site at autotrader.mobi. The mobile version lets you search a database of over 400,000 vehicles for sale by make, model and postcode. The site is free to use for buyers, no registration is required and listings include the seller's contact information.
To place an ad you will need to visit AutoTrader's full site at autotrader.co.uk Ads are not free. Prices range from £9.99 for a 2 week online-only (including mobile) listing of a vehicle priced under £1000 to £44.00 for a 3 week listing of a more expensive vehicle with the ad appearing simultaneously on the web and in the print magazine.
There's an AutoTrader in the US too. It's under different ownership but uses the same business model as its UK namesake with a free shopper magazine and web and mobile sites at AutoTrader.com and m.autotrader.com respectively