Another scam is extra virgin olive oil. Almost all of the ev-olive oils that you buy at supermarkets in the US are fake [0]. It's basically lower-grade olive or vegetable oil with some added green chlorophyl for color. UK supermarkets aren't faring much better [1]. It's all due to mafia control of the oil markets in Italy. 60 Minutes did a report on it recently and they even tested oils for fakes [2]. It's extremely difficult to tell if your ev-olive oil is fake without chromatography/spectroscopy equipment but some people try [3].
[0] http://time.com/money/4326354/fake-olive-oil-food-fraud/
[1] http://www.telegraph.co.uk/news/worldnews/europe/italy/11988...
[2] http://www.oliveoiltimes.com/olive-oil-basics/mafia-olive-oi...
[3] http://www.foodrenegade.com/how-tell-if-your-olive-oil-fake/