The term 'unverified' simply means that the related website is blocking crawlers. In such cases, it becomes difficult to check the presence of certain links. However, some checker tools are able to verify at least the reason for the blockage through a set of specific codes. Also, this does not always mean that the website in question is a 'sneaky' or malicious one; sometimes, the problem is simply due to technical issues. These can be tracked in the checker's dashboard.