Olive oil is very good whether Spanish/Greek/Californian.

The processing is the problem and the cultivation.

In my religious/fasting cakes I use olive oil and in my non-religious cold pressed sunflower oil instead of butter/margarine.

Spanish person here. Spain is the biggest olive oil producer in the world. So big that Italia, and others buys the oil and pack it with its own label. There, is where some adulteration may come from. In Spain you can buy directly from the producers called "Cooperativas agricolas".