Since eBay is a marketplace for third party sellers, it is at the discretion of the seller to include a certificate of authenticity. EBay offers a filter in searches that narrows results to only certified silver dollars and only those certified by specific companies.
Within each product page, in the item description, the certification company and number are available. The item description allows sellers to include further information on the condition and certification of the coin.
EBay protects the purchase of an item with a fraudulent certificate of authenticity with the eBay buyer protection program. Buyers have 30 days to file a claim. Purchases made through PayPal are protected for 180 days by PayPal.