The best form of advertisement on an auction site is a good reputation for quality goods and no reports of failure to deliver etc. Do either of the sites stop you from having a link to your site in your profile? That's the easiest and best way to promote interest in your site, someone buys from you or likes the dvds you are selling, they look in your profile and see the link, link gets clicked and the buyer now knows where your site is and the full scope of your DVD stock. failing that you can always use your site name (example dvdsales uk) as the account name like here
EBAY link.
The search engine scoring can be affected by use of keywords in the HTML of the site, good use of HTML coding can make a big difference in your listing on a search engine.
After that you can always try getting yourself listed on free directory services and sites local to you, build up your custom locally as well as further afield.