I'm always a little dubious because of the financial incentive to cut unrefined oil with some amount of cheaper refined oil, but I don't have any idea how much this actually is done with olive oil.

The label usually won't say what the process was in my experience, but you can look into what processes are used for refined olive oil. Just avoid refined oil entirely. And if I see "olive oil" as an ingredient in something or at a not-high-quality restaurant, I'd assume it's refined.