The easiest way to guarantee that you’re buying a quality bottle is to make sure it says ‘extra virgin’ on the label. Other labeled indicators of quality extra virgin olive oil are phrases such as ‘first press’ or ‘cold pressed’. If you can find it, check the harvest date on the bottle. Ideally, the harvest date should be less than a year from the date you are purchasing.  If the bottle states the percentage of acidity, the best extra virgin olive oils are less than 1% acidity. At the end of the day, it's always a good idea to taste the extra virgin olive oil to see for yourself what the flavor and mouthfeel is like.