One of the hard truths about dealing with customers is that they don't care whose fault it is. They're just angry and they want a resolution.

In practice, you can't simply divide customer problems into self-inflicted and company-inflicted and decline to support the customers' self-inflicted problems. The line between the two types of problems is too blurry to enforce, but the reality is that customers don't care either way. They just want you to fix it, and they expect your product to prevent them from shooting themselves in the foot in the first place.

Doesn't matter if it's their fault. If their monthly recurring revenue is high enough, they'll make it your problem. I've seen it happen.

It doesn't really matter whose fault it is, it's still your business.

And you probably keep better backups than they do. I've had this happen plenty of times. Free backup restore test.