Airline systems are complex and many are outdated. There are also humans involved in the inputting of fares, taxes and fuel surcharges. The result – mistake fares!
But who has the time to search google flights in the hope of a mistake fare – certainly not I!
There are other considerations: The airline may decide not to honour the mistake fare – even though you booked and paid for it and have confirmation. So don’t start booking non-refundable hotel rooms off the back of a mistake fare.
I’ve recently found a site called http://www.secretflying.com/ that appears to do the work of finding mistake fares for you. So far I haven’t found anything that I want to book, but I’m going to keep checking. What they don’t highlight enough on their site is that you shouldn’t call an airline and ask to book that amazing business return to the Maldives for the price of a restaurant dinner – book online!
The only part that worries me is that the website isn’t really a secret – anyone can find it. So if I ran an airline, I’d have someone check that site a few times a day, just in case they found one of my airlines error fares.