DoS is an understandable concern, but charging for a service is probably one of the least sensible ways to prevent it. To me, it just looks like the most profitable and impeding hurdle that companies can set up to prevent users who want to access their own data. I would be frustrated if any application made me pay even a small fine because they suspect a DoS attack. For example, entering my credit card info because I've searched a phrase too much just isn't efficient.