Actually, my supermarket has often "comped" an item where a bar code shows no price. This issue of "an unbelievaby good price" comes up frequently in the travel business. Most companies will honor the fare rather than admit it is a mistake, which could undermine public confidence in the integrity of their online systems (which contain much personal information as well as pricing info). But unless you are willing to go to court, the airline holds all the cards and if they won't honor the price you're effectively stuck.