When looking for a mystery shopping company you have to be careful. There are quite a few companies that are not good to work for, they don't pay you, you don't get any assignments, or they are just not nice.
One company that I love, and I do occasionally do shops for is ICCDS. They pay $10.00 per shop, and sometimes they reimburse $2 or $5 if you buy something.
If you want more info or to sign up you can click here!!