I have a hard time believing Norma would open themselves up to such liability in today's litigious world.
They're not some fly by night operation.
Then somebody is seriously screwing up in the shipping department.
Unfortunately, the penalties for shipping an unmarked hazmat would still apply. They are liable whether it was intentional or accidental.
They might be a little more lenient if it was one mistake, but if it is determined that it isn't a one-time deal they could still be fined and loose their hazmat shipping account.
Shipping companies don't take this kind of stuff lightly - they can't afford to, because the DOT takes a very negative view of shipping reg violations.
Unless they have changed in the last couple of years, the shipping companies (UPS, FedEx, etc.) in addition to requiring that the shippers employees go through a bunch of training, and charging the shipper an annual fee to be certified to ship hazmats, they charge the shipper an extra fee for each hazmat package to cover their costs in extra handling, processing, training, etc. for handling hazmat packages. So if the seller/shipper advertises free hazmat, it means they are covering that fee for you out of their own pockets - because I can just about guarantee you the shipping company isn't waiving that fee.
All of that is in place to ensure compliance with DOT regs regarding transporting of hazardous materials on the public roadways. Staying compliant with regulations costs money.