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www.rcfp.org]
Outlines which states require "all party consent" for audio recording. Needing a PI license is an entirely different matter. As far as I know, only Nevada requires that mystery shoppers be affiliated with a company holding a PI license and have a card stating tha they are recognized by local law enforcement for this affiliation.
Please also do a search on video and on PI here, for many posts on both subjects.
Based in MD, near DC
Shopping from the Carolinas to New York
Have video cam; will travel
Poor customer service? Don't get mad; get video.