The eBay program is now available in your HubPages Earnings Program. And soon Amazon will be available via the HP Earnings Program too.
With eBay you get paid for quality clicks in addition to sales. Quality means that even if they don't buy, but if they bid and lost, it pushed the bid price up and someone else ended up paying more for an item. So eBay gets a bigger fee for the sale and therefore they consider this a quality click that came from you.
Go to your HP Earnings Program page to sign up for eBay. Click the Earnings tab under your account.