This is a list of mystery shopping companies that I have worked for and gotten paid for and had no problems whatosever:
All of the companies above I have worked for. There is also a GREAT list of companies at Volition. I've applied to become a shopper for a lot of these companies also, but there ae a lot of them that just don't have shops in my area. So I can't say one way or another how they are, but this is a good list also!