There was an article on this a while back. Ebay is a top ten visited shopping site/ website in general. I would say it gets millions of hits every month from unique surfers. They can boost their earnings by selling ads/banners on their site. However, they do not want to alienate seller by advertising/linking ad to 3rd party sellers i.e. cars or dell computers or whatever. If ebay started to link ads to companies that compete with sellers on ebay, they might lose more business from the backlash then they would from the ad revenues. So, they sell ads to fast food joints or advertise movies rather than companies that might compete against sellers.