You sold a tool to the user with a claim on how it would work. If the tool behaves wrong or does not works as intended then as a manufacturer you are liable for the defect/damage not the end user who used the tool.
Reasonable but not what parent was arguing:
> Don't know how to operate a power hammer? don't care, any problems it causes are still your fault.
But the tool wasn’t sold. The tool wasn’t even rented out. It remained the property of, and in the possession of, the toolmaker at all times.