Earlier quoted context omitted.
Cheap olive oil from Costco is not counterfeit. Cheap honey from Costco isn't counterfeit. Cheap vanilla from Costco is...once again, not counterfeit. Moral: Buy things from Costco.
Olive oil should be used within a reasonably short time of opening, which makes Costco-sized bottles less practical. We buy honey and vanilla extract from Costco, but we don't use olive oil anywhere near fast enough to justify buying Costco-sized jugs.
Olive oil (and all cooking oils in general) are the opposite of wine - once bottled they start degrading and any additional exposure to air, light, heat degrades them further.
What degrades specifically? Usually it's the nuanced flavors and health benefits of good extra virgin, it'll usually be fine for cooking but you're losing out on the purposeful decision of using olive oil over vegetable oils (gross)