Mystery Shopping a Viable Source of Income?

My mom called me excited about a job offer she had for mystery shopping, but I have never done this type of work before. How does it work? Do you have to put your own money into it to start? I am not sure who the company is but they want her to pay $40 upfront to get a list of companies and training. Is this normal? Any help would be greatly appreciated.

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    Update: It was a scam. She never found out the actual name of the company, and I told her to verify people they have worked with or and why they are charging for the list when other companies offer the lists for free or email you when a shop becomes available. Oh well you win some you lose some. Shame on them for trying to scam my mama. Always do research.
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    About Celeste Whitehead
    Current: Spring Hill, Florida
    Birth: August 26
    On Moms.com since: Aug 5, 2013
    Stay at home and work at home mom of two loud, crazy, adorable kids that are the center of my entire world. We all live together with the love of my life and the father of my children in sunny Florida with 3 of out four-legged kids.