The store is under no legal obligation to sell it to you, just like you're not obligated to buy it for that price. Depending on the situation, that might be false advertising they could get in trouble for, and obviously you're not committing a crime if you don't know the real price, but if someone says "oops, that's a mistake", and you take it anyway and give less money, that is theft in most states.

True. They can keep you out of the store. Under some circumstances they can indeed keep you out of the store. However it's still the US and the reasons for keeping people out of stores are restricted, and we've all learned in high school why.

But, once inside, an offer is made through the pricetag and accepted the sale is final. Before payment, before ... The whole point of price tags is making an offer. So if you are inside the store, take the good, and accept the sale at the price on the tag, obviously a court will rule both sides are in agreement about the sale and price at that point (NOT at the cash register) and that's that.

Additionally, money legislation makes cash the universal cop-out. You can always choose to settle a debt through cash. And that debt is what's on the price tag, the offer that was accepted, nothing else. In other words, the cashier and the manager, hell the CEO comes down and refuses? Give them cash and walk out with the goods. Perfectly legal thing to do. The sale was already final, and this settles the debt. Done and done.

This is why messing with price tags in stores is such a serious offense.

This goes pretty far in law. You can actually go to the IRS, ask to pay with cash money, and they'll let you pay your tax bill cash. Cash is the universal cop-out.

https://www.irs.gov/payments/pay-your-taxes-with-cash