How does Amazon know that author you're reviewing is a member of your family?

It's easy to see why Amazon would want to edit out biased reviews, but how can it know who is biased? And then there's that lady who has published an average of 7 reviews a day for over a decade, 99.9% of them 4- or 5-star — can anything be done about her?

ADDED: One thing Amazon can see easily is where you ship packages, presumably presents. It has names and addresses, so if it has the author's name and home address, that would match up.