If you are providing a valuable service/product there will always be people trying to "cheat" the system and get in. Providing a free trial period is an industry norm and over time users may sign up for more than one trial but that will get old fast. 

I would worry less about ensuring authentic users and focus more on providing that great content. If you're doing awesome work then most of your users will appreciate and pay for it. 

Another thought would be to limit the amount of content someone can consume even on a trial. Maybe they get 50% of the content or 80%, or maybe you can find some other value add to give paying users.

Good luck