Eggspots are clues, although females may sport them, a males may be more defined and have better color. Acei and Labidochromis caeruleus are tough ones. Watching your fish helps, but even when you think you have it figured out, they will surprise you. Aulonocara are tougher when they are young. The dominate male will usually start showing color anywhere from 12 - 18 months of age.
Subdominate males are more difficult.
If you suspect you have one, you might want to move out the dominate male and see what happens. If nothing happens, I would say you have a good possibility of having a female. Sexing fish just takes time, and I think one of the main keys is observing your tank, and getting to know your fish up close and personal.