piatkow - 1:35 pm on Feb 9, 2013 (gmt 0)
I agree about using noarchive. You could easily get bad mouthed on forums by the technologically illiterate for supposedly advertising vehicles that are already sold. Don't forget that that sort comment hangs around for years and somehow always stays high in the SERPS even if out of date.
Any indexed page will be returned in the SERPS until the search engines spider the site and decide that it is gone. If people say that they are unable to reach the site it suggests that you don't have a custom 404 page (can you do that for a 410? I have never needed to know). Remember that links may be emailed or posted on forums as well as being found in SERPS, you really need a definte page offering a site search for an alternative vehicle.
I am not sure about keeping "sold" pages hanging around. The proportion will build up and will start to give the impression that you don't have any real stock for sale.