

Patent vs latent defect. Any issue with the product that the customer could reasonably identify before suffering harm is the customer’s responsibility to avoid. The vendor’s liability here is the cost of the burger. The vendor is not liable for the harm arising from the customer’s failure to look at the food they are about to eat.
The vendor is responsible only for harm caused by defects the customer could not reasonably avoid. Hiddent, latent defects.
If this is a case of subrogation, as I suspect, the customer acquired insurance coverage for the purpose (in part) of mitigating harm due to their own negligence. If this is the case, it is that insurance policy that is liable for the harm caused by the customer’s failure to verify the burger met their requirements.
I would call it “frivolous” when the primary purpose of a case seems to be for two teams of lawyers to generate billable hours for eachother.