Depends on the rules of the country. Under FAR, yes. In Oz there must be a fuel guage calibration card that gives the correct** quantity for the gauges divisions.
Even so, most GA gauges measure [i]volume[/] but fuel consumption is by weight. That in itself affects how accurate the gauges can be to determine endurance.
As for the accuracy of a fuel gauge, the certification requirements aren't that high a hurdle to jump. What might seem rather poor can still be within requirements without necessarily being faulty.
**But then ground attitude doesn't have to equate to flight attitude. Oops, another contributor to fuzzy accuracy.