There are jurisdictions where a price tag in the store is almost always assumed to be an offer (a.k.a "public offer") and the company is legally required to honor it. In some circumstances the employees who screwed up and put the incorrect price tag will bear most the financial responsibility which sucks. That's why you shouldn't do it if you get the chance - it's not a legal loophole to stick it to a corpo, you're just ruining the life of some poor overworked retail employee who misplaced the price tag.

And yeah, the good faith part is also really important. If the person has asked a couple of questions to a chatbot, got recommended some products, asked if there's a discount available and then got an 80% discount out of the blue, got excited and made the deposit, it would probably be enforceable. If the customer knowingly "tricked" an LLM into giving out a bogus discount code, it would be very dubious at best.