Hello and Welcome!
If you have not done so already, I suggest you read the "New Shoppes" area of this forum. It has a tremendous amount of information that will really give you a good sense of how large the mystery shopping world is - and how to go about becoming successful as a shopper. There is also a large list of legitimate companies linked at the bottom of this page. Other than that, this forum is full of folks who have been shopping for years and are willing to share some of their acquired wisdom. Feel free to ask as you have questions.
Hard work builds character and homework is good for your soul.