meta-search sites in travel (Skyscanner, etc) have the same problem of out of date cached information from the merchant. not solvable in practice because there's so much traffic volume and low rate of conversion that you must cache for cost reasons.
Those typically have a list of vendors from lowest to highest (cached) price. IME the prices are correct more often than not but if the best deal has expired you can still check out the next best one.
Well, my point is that there is always a certain level of incorrectness and that can never be fixed because of the cost of retrieving up to date pricing and availability.
