It is generally impossible to perfectly police a site the size of the stack exchange, so site is moderated automatically by users(and some dedicated moderators) via the review system.
Invariably this means some amount of error,since there is some fuzzy logic the idea being that over time more people will downvote then there are sock puppets. All questions are designated as important when they are new, but this status very quickly degrades if they are not "popular". This means a question should show up, be down voted, and then drift into oblivion without causing too much disruption to the site's usability.
Since most users are either searching a specific question, and not arriving on the site to just see "what's hot", there is a fairly small pool of questions which both answer the question and are popular, these will float to the top of a search.
Users which repeatedly receive bad reputation are banned
This means generally speaking it is not necessary to manually weed out sock puppets, since the accounts they promote are automagically found to be disreputable by the community.
On Meta Stack Exchange there exists sock-puppets tag. Maybe if
somebody has time to have a look at some of the posts there, they
could be able to answer your question in detail. This question seems
relevant: How can you detect if users have created sock puppet
accounts? This one also mentions briefly what is expected from mods:
How should sockpuppets be handled on Stack Exchange? – Martin Sleziak