I agree that it's not good faith, but speaking from the position of someone who has offered self-service signup... that's what customers did. They'd create an account, start using the service, ignore emails from their account manager, and then dispute the bill when we charged their card. This is rare, of course, but it is something you have to expect when you give someone free reign to spend money and then bill them at the end of the month.
It's something you have to expect, and kind of gauge how much money the customer has and send them lots of email as they approach a limit, and make it very clear in the UI that money is being spent that they will soon have to pay. Even then, who knows what people will do. It's bad faith on their part; you, the service provider, are the ones penalized.
this is not good faith B2B behavior. i'd be surprised if 1% of B2B usage based billing customers behave like this.