Get your typing fingers ready! Welcome to the forum. Sign up with as many companies as you can. Many are located under "Official List of Mystery Shopping Companies" at the bottom of this page.
My success came from personal research and lots of reading. I've been doing this for nine years and still find companies to sign up with after an hour or more of research :-)
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Gold Certified
507+ Sassie Shops
Shopping South Florida since 2007
Own PV-500
IMSC132