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This page in a nutshell:Never assume a user is a sockpuppet – it can create bad feeling and violates Wikipedia:Assume good faith. Wikipedia has its lurkers.
A lurker is someone who creates an account on an Internet forum or a wiki but does not participate or post much. They read it, but only participate if and when they feel it is worthwhile to.
Wikipedia has many lurkers. If you see an account that seems to know Wikipedia policy and formatting well for a new user, don't assume it's a sockpuppet – the user may well be a lurker, or a friend could have taught them about Wikipedia. Some users may well be friends/acquaintances of another editor, and not sockpuppets. They may also have a lot of experience from doing edits as unregistered users, or switched accounts for reasons not related to sockpuppetry. They may even have done a substantial body of work on another Wikimedia project, such as Wikibooks or Wikiquote, before actively participating here.
Be aware that new users to Wikipedia come in many different forms, and people are introduced to Wikipedia through friends/family or in school/college/university.