Usually when people say "selling user data", they usually mean "monetizing user data". There are four levels to doing that: - Level 1: Monetizing aggregates. A

Usually when people say "selling user data", they usually mean "monetizing user data". There are four levels to doing that: - Level 1: Monetizing aggregates. Aggregating lots and lots of data, running statistics on all of it, and selling the outcome. Example: An online streaming site that sells TV analytics to TV channels. - Level 2: Selling proxied access. That's the Twitter/Facebook/Google ads model: Allow interested parties (advertisers) access to an audience, but they never are directly told "Mary Jane is a 33 year old woman with 2 children and an income of $80000/year." - Level 3: Selling personal data. This is what people think is happening in level 2, but is much rarer than it sounds. For example, let's say you have influencers on your site, you'll sell to potential sponsors data about that influencer. Or sites with personal statistics and insights that will sell access to it to their users' competitions (a known practice in sports services). - Level 4: Selling confidential data. That's where we're talking the really shady/illegal stuff. Gathering emails/credit cards and selling them to spammers and fraudsters, that sort of stuff.