There is a lot of luck involved (like Telfes said). Fares discovered at say 11am are sometimes corrected/removed by 3-4pm (of course this varies). Your best bet is to look on the MR (Mileage Run) forum and look on the first page for VERY ACTIVE threads. Often, the incorrect fare threads get LOTS of posts very quickly.

While you're looking/waiting for fare errors, please take a look at some of the other forums on FT and feel free to contribute

Welcome to FT