Your best bet is to buy California olive oil with a harvest date on it. I buy whole foods EVO and it's not cheap at $12.99 a bottle but I know it's the real deal. One of the tip offs of fake olive oil is it will smell faintly like playdough. If the olive oil smells moldy, musty, or winey, it is most likely to not be real olive oil. The real stuff has a fresh floral scent to it.