Then they need to start a team dedicated to finding a good way to let customers halt spending at a given limit with minimal impact on their operations.
They already win on UX (okay, okay, it's an opinion ffs), but unlimited liability makes a lot of people very uncomfortable. Those two actions would go a long ways towards demonstrating good faith in that area.
If it would cost too much, maybe they could present it as an easy way to cut expenses at the same time that they introduce a small price increase. This is a common and long-standing complaint/feature request.