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> it may be that common law prevails as you say in most transactions despite the states with regulations

As already mentioned IANAL, but I would take an educated guess as follows:

The specific regulations to which you refer are in effect consumer protection regulations.

Ergo, they are there to protect the consumer against malicious behaviour by unscrupulous traders such as false or misleading information.

Any reasonable judge in a courtroom will likely agree that incorrect display of pricing on a shelf (or website or catalogue) is (in the absence of evidence to the contrary) likely to be an inadvertent error with no malicious intent. And therefore the common law would prevail.