Extra virgin olive oil for the purpose of my theme, the ways in defining quality is just as similar as differentiating between choices.
First, the dates. Harvest year (usually falling between Fall and Winter) and expiration dates should be enough to portray the product life, usually up to 2 years (though best if used within a year for consistency in taste and quality). With those two items already in mind when you buy your oil, you could predict how old the oil is (or how long it’s been on the shelf) and how much longer is left.
Another point would be to check which region or country it’s from. This is a whole new topic which may get a bit ugly, but in short the variable geo-climate, technique, and olives could alter the definitive quality right away. Mediterranean climates are favorable due to its abundant sun, cool climate, and the natural hilly geographical location not easily manipulated elsewhere in the world (attempts in the US and claims of similar to near perfection is debatable). Even the discussion of Italia’s best is difficult to analyze. Actually I dare you to ask any Italian where they think has the best olive oil and I guarantee every single one of them will assume their origin as the best. That’s why I wouldn’t want to start an argument siding on one over another.