The Ebay affiliate program works differently to CPA models, running a 'quality click pricing' model.

Ebay evaluates the traffic sent to them from each site or publisher and then assigns a value to that traffic based on its quality. The quality of the traffic is rated on both the short term value (the amount of incremental revenue generated by purchases, PayPal and advertising, as well as the engagement of those users on eBay. In particular purchases that happen as a direct result of the publisher’s marketing efforts) and long term value (a measurement of the revenue that new user generate on eBay beyond the first few days after a click) of the traffic to Ebay.

At the end of of each day an EPC (earnings per click) amount is posted for each publisher, this is then used to value the following days traffic.

For more information see https://publisher.ebaypartnernetwork.com/files/hub/en-US/quality.html.