Warranty is the insurance for end user against loss of money when submitting payment on site secured by SSL certificate. Warranty is provided by issuer of SSL certificate (certificate vendor). By offering warranty vendor takes the responsibility to verify applicants prior to issuing certificates. In instance when end user is charged fraudulently, vendor is to provide reimbursement according to their terms or service. Depending on type of certificate vendors have different amount of money as warranty.
More information on warranty provided by Comodo is available at Comodo Repository page.