In contract law, for a contract to exist, there must be an offer and an acceptance. I learned in law school that a price tag isn't an offer. It's an invitation for the shopper to make an offer, which the store is free to reject. So, if an item is mismarked, the clerk can tell the customer, in effect, that the offer is rejected and an invitation to make an new offer, at the correct and higher price, would be entertained.
Of course, a smart retailer will sell the good at the mismarked price, since that will heighten the store's good will.
Now, there are various laws and regulations about what happens, if a retailer has the wrong price listed. A retailer may have to sell the item at the marked price. Then the retailer will correct the price for future customers. For a price listed in a newspaper ad or flyer, the retailer may have to display the correction in the front window or by the register, as well as buy ad space announcing the correction.
But, based on contract law, a very low (and incorrect) fare offered by an airline is merely an invitation to make an offer.
Now, if a carrier is smart, it honors those incorrect fares while getting it's IT
department to correct the fares in the system ASAP.