"make the manufacturer or the reseller liable for selling an unsafe product. "
I agree, but that is already the case, I believe.
Any gun that undergoes Rapid Unplanned Disassembly when fired should be grounds for massive compensation.
Any gun that fails to fire in an emergency when the trigger is pulled... that requires more work, as you would have to prove that the ammunition wasn't faulty, you hadn't left the safety on, etc.
That's also a reason why many service pistols do not have a safety - there is a chance that it will fail to function due to user error in an emergency situation, which is very unsafe.