But how do you sell this to the user? "We will give you full, unfettered access to this application for free until you begin to really rely on it, than we will

But how do you sell this to the user? "We will give you full, unfettered access to this application for free until you begin to really rely on it, than we will charge you" Doesn't sound quite right from a marketing perspective. And how do you know when your users have reached the stage when they are sold? Ask them? "Are you ready to pay for this now?" I'm not meaning to be critical, I would really like to know!