I'm still new to mystery shopping, but as far as I understand the company, they are a company that you pay to search for jobs. They do not pay you directly, nor are they a mystery shopping company themselves. They are similar to Jobslinger (if you are aware of that site), only they charge a fee to view and apply to certain jobs.
You can get around paying them by signing up with many companies directly. I found shadow shoppers initially when I started my hunt, but didn't like the idea of paying a fee. So after googling more, I found this forum and signed up with the majority of the companies that are positively discussed here. I do not pay shadow shopper to gather the info for me, I do the research myself.
Mostly, I believe the fee is to cover the convenience. But I'm sure someone more experienced can answer your question better than I can.
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