The idea behind discount usability methods, like heuristic evaluations in particular and expert reviews in general, is that it's better to uncover some usability issues --even if you don't have the time or budget to test actual users. But, can we trust heuristic evaluations? How do we know the problems evaluators uncover aren't just opinions? Do they uncover legitimate problems with an interface? How many problems are missed? How many problems are false positives?