Hmmm. That's pretty wild.

I was a manager at a big box store for a while, and the general rule of thumb was to verify an error in pricing and then just mark it down at checkout for the client.

Usually, it was an old tag that was left up.

Or

It was an ad that the customer misread.

I don't recall there being a one-time price discrepancy law forcing me at penalty of jail to take 50 cents off a pack of pencils, we just did it because it's better in the long run to keep the customer happy than it is to get in a fight over pricing. If there was someone who was serially abusing this hospitality, then we might have a talk with them, or ban them from shopping in the store, like when someone was stealing our discounted labels and then putting them back up when they were in the store weeks later.

I also wasn't in Massachusetts...