Unroll.me made some money from showing their users advertisements. Many of their users assumed that this was the service's only source of revenue. They also sol

Unroll.me made some money from showing their users advertisements. Many of their users assumed that this was the service's only source of revenue. They also sold their user's data [1], prompting backlash from those users. How can you be sure that a service, like Grammarly, isn't selling it's user's data, or will do so in the future? [1] https://www.nytimes.com/2017/04/24/technology/personal-data-firm-slice-unroll-me-backlash-uber.html https://www.nytimes.com/2017/04/24/technology/personal-data-...