Take into account that typical cost per click on a banner network is 25 cents you have the makings for a great return on investment. Many auction sites, eBay included, provide an About Me section. Again it's time to break out your list of links and point that page toward your sites and talk about your business. Be informal but be professional. Make sure any outbound links are relevant to the product you are selling.
Some auction sites prohibit any up selling or affiliate type of links inside the auction ad.
Many small businesses are ready to strike an alliance. Power sellers see, talk and influence a lot of people. For example, you could provide a computer seller a discount coupon for your repair service. This is the easiest way to get the word out about your site. Make sure your auction is stuffed with keywords that relate to your topic.