Orange you a lime?

Stopped by the market to pick up a lime to make limeade for my cold. Small green round fruit, right? Well, got home, only to find out it was a tangerine. Don't be fooled. Tangerines in Taiwan are green. And they can be small, like a lime...
http://www.omg-facts.com/Science/Oranges-Are-Green-Not-Orange-When-Grown/52278

How are you going to know  if qing pi is really qing pi and not chen pi?