I think this site will do well with some marketing to Mac users. Try to get linked on Mac sites. Buy these links if possible. But first, write more text for the home page to help yourself get organic rankings on the search engines. Also conseider PPC for obvious keywords such as "used macs". Don't worry too much about design issues, mac lovers will go straight for the goods! Best of luck with the site.
I currently have an Adwords campaign running which brings quite a few visitors to the site every day. Thanks for the other tips Rod!