[swalling]

Adulteration of olive oil typically happens in transit/shipping by wholesalers, not by producers. Spanish or Italian olive farms aren't diluting with corn oil or whatever during production on the farm/when pressing, it's by aggregators who are buying and selling oil in bulk by volume. So if you're buying olive made, processed, and bottled by a single farm whose origin is local you're structurally at less risk than a generic "Italian" oil or one that says the country of origin could one of 3-4 countries. Also California has a mandatory sampling and testing program https://www.oliveoilcommission.org/

If you want to go deep on the topic, this is a great read: https://www.goodreads.com/book/show/10955085-extra-virginity