A sign posted on the door of a Vancouver-area bong shop ordering police to keep out didn't prevent undercover officers from targeting the store in a sting operation, says British Columbia's Appeal Court.

Timothy Felger, who owned a store named DaKine in Abbotsford, B.C., and employee Natasha Healy, were charged in 2009 after undercover officers visited several times and bought marijuana, later returning with a search warrant.

Felger and Healy argued a sign on the door that said, in part, "No Police Officers Allowed" should have prevented undercover officers from wandering in and purchasing pot.

The trial judge agreed and acquitted the pair in 2012, concluding the sign meant the officers should have obtained a warrant before entering.

But B.C.'s Appeal Court overturned that decision this week and ordered a new trial.

"An objectively reasonable expectation of privacy in a retail store could not be achieved simply by posting a sign excluding law enforcement officers," wrote Justice Nicole Garson in a unanimous judgment.

"There is an element of artifice in the respondents' claim to privacy in a place in which they were publicly and brazenly selling marijuana, conduct that is currently unlawful

According to the Appeal Court judgment, Felger's lawyer wrote the Abbotsford Police Department a letter in 2005 demanding that police stay out of the store without a warrant. He then put up the "No Police Officers Allowed" sign, which also listed the badge numbers of two beat officers who worked in the area.

In 2009, police received a complaint that the store was selling marijuana to minors, prompting several investigators to target the store. They bought varying quantities of marijuana on five separate occasions.

A search warrant was executed in May 2009, and Felger and Healy were each subsequently charged with three counts of marijuana trafficking. Felger was charged with an additional three counts of marijuana trafficking and one count of possession for the purposes of trafficking.