There are a lot of fakers out there. Here's how to find the best olive oil for your buck.

Shop where you know there's inventory turnover
Buy for use within two months
Opt for oil in dark glass bottles or in tins
Choose "extra virgin olive oil", it's the purest, least processed and most flavorful type
Be wary of bargain-bin oils (less than $10 a liter)

More resources include the North American Olive Oil Association and TruthinOliveOil.com run by journalist Tom Mueller, author of the book Extra Virginity: The Sublime and Scandalous World of Olive Oil.