How can I troubleshoot a 404.3 error when deploying a WCF service to IIS?

First, verify the WCF service configuration in your application's web.config file. Ensure the endpoint addresses specified in the service definition match the URLs being requested by the client. Double-check that the service is actually deployed to the correct IIS website and directory. Also, examine the IIS application logs for more detailed error messages that might pinpoint the exact cause of the mismatch.