The difference is that a paid service can survive without selling something. With a free service that isn't offered by a charity, they need to generate revenue

The difference is that a paid service can survive without selling something. With a free service that isn't offered by a charity, they need to generate revenue at some point. You just have to figure out what they're going to sell. My guess is that Mint won't really do this. But it's an important risk; I'd feel way better about them having my data if someone out there was paying $5/month to use Mint.