Complaint / review text:
I can't speak for Shadow Shopper's member registration policies or paid memberships, but I can say that I work for a legitimate mystery shopping company and regularly post jobs to Shadow Shopper's database. I also occasionally purchase contact information for shoppers in an area that I am trying to assign. It is worthwhile to register with Shadow Shopper as a Bronze member so that you at least have the chance to receive e-mails from folks like me.
As a mystery shopper myself, the best resource that I can recommend is mspa.org. Every company posting there has been vetted by the organization. I have never had an issue accepting assignments from companies posting there.
As a general rule, you should never pay anyone for an opportunity to shop. I personally would not have a paid account on Shadow Shopper, as it is easy to find jobs without their services. The way that they *should* be making money is by having shoppers with free accounts and schedulers paying to contact the shoppers. That's just my 2 cents. Hope this helps!