Advertisements
An business model for an advertisement company following the Solid Philosophy could be that users voluntarily subscribe to some advertisement broker. On a third party system the match is made between personal interests (shared by the user) and advertisements. Both the advertisement broker and the users can receive a little bit for every advertisement shown.
Because of the third party, the advertisement broker doesn't need to know the interest of the user itself, but it can still make a match through the third party.