A good pair of black earrings has weight to it, even the small studs. You pick them up off the dish by your sink and there's a little drop in your fingers before you've put them anywhere near your ears, a sense that the metal or the resin has some substance rather than being stamped out of foil. The clasp should click shut with a bit of resistance, not the loose, rattly give that tells you it'll be in the bottom of a bag by Christmas.
Black earrings earn their keep differently depending on the time of year. In winter they sit well against dark coats and scarves without getting lost, which is the whole point, since gold or silver can disappear into a navy jumper but black holds its own line against black. Come summer, against bare shoulders and a tan, they read sharper, more deliberate, and that's when cheap ones show their age fastest, because sun cream and sweat get into any weak plating or glue and the colour starts to go patchy or grey rather than staying properly black. Keep them out of the shower, out of perfume spray, and wipe them over now and then with a soft cloth, and a decent pair will hold its colour for years rather than months. Store them somewhere they're not touching other metal pieces in a heap, because that's how black enamel chips and black plating scratches down to whatever's underneath, usually a dull gold that was never meant to be seen.
Where black earrings struggle is against anything already busy or already black in a different finish, patent against matte, for instance, which can look like two different decades arguing with each other. They also don't love competing with a statement necklace in the same colour, it ends up reading as one block rather than two considered choices. The difference between the ones worth having and the ones that end up at the back of a drawer is almost always in the finish: a true matte black that's been properly coated holds up, while a cheap glossy black laminate scratches to reveal plastic within a few wears. Good hardware has a proper post, a backing that doesn't wobble, and clasps that feel engineered rather than glued on as an afterthought. Resin ones should feel cool and solid, not light and hollow like a sweet wrapper.
Next time you're looking, pick them up before you check the price, and see whether the weight in your hand matches what your eye expects.