"Extra virgin" is not a marketing phrase. It is a real, measurable standard covering how the oil was extracted, its acidity, and its defects. That is the good news. The other news: independent tests over the years have repeatedly found imported oils on US shelves that failed the standard their labels claim. The label is a promise, and nobody checks the promise at the shelf.
What actually tells you something
A harvest date on the bottle is a good sign. Olive oil is closer to fresh juice than to wine; it degrades with time, and producers proud of their oil tell you when the olives were picked. "Best by" alone tells you when the seller would like it sold, not when the oil was made.
Dark glass protects the oil from light, which degrades it. Clear plastic does not. A producer who bottles in clear plastic has made a decision about priorities, and you are allowed to notice it.
Words like "pure," "light," and "olive oil blend" are marketing, not quality grades. "Light" refers to flavor, not calories. "Pure" has no enforced meaning on an olive oil label. If the front of the bottle is doing a lot of talking, read the back.
Why a price-truth company writes about olive oil
Because it is the same problem. A label makes a claim, the claim is hard to verify at the moment of purchase, and the gap between the two costs shoppers money. We started with the version of that problem we can solve completely and automatically, whether an Amazon price is actually a deal, and we are building toward the harder versions: tools that read the official records and tell you in plain language whether a product is true to its label.