Select people, sports, media, entertainment, and government accounts are eligible for verification if they can prove their authenticity and meet specific requirements for having a Verified Badge on their Facebook account.
Twitter approves account types maintained by users in music, acting, fashion, government, politics, religion, journalism, media, sports, business, and other key interest areas.
Instagram do verification for public figures, celebrities, and brands. Accounts representing well known figures and brands are verified because they have a high likelihood of being impersonated.