Some black olives are not black olives, meaning they are not ripe, but instead green olives that have been made black through a certain treatment with lye and ferrous gluconate. The former for ripening them and the latter for fixing the color. If you compare the two, you'll notice quite a difference in colour and taste.
Black (ripe) olives does not look like this ...
But rather like this. Notice how the colour is more towards a brown or dark burgundy and also varies between olives.
These olives are also not pitted, and you will find that pitted olives often will have lower overall quality (not being real black olives e.g.) and having a slight aftertaste of cardboard.
In short: Yes. At least here in Sweden it is a lot easier to find bad olives than good ones.