When the evaluation period is over constructors of classes included in the component will start throwing an exception. The exception will show the message about the end of the trial period.

For example the Rebex SFTP will start throwing a SftpException with following message:

Trial version of Rebex SFTP for .NET has expired. Please consider registering at http://www.rebex.net/.

When it happens you'll have to replace the trial dll with the full ones.