Right below your post is a link for more discussions about Shadow Shopper.
There are some shoppers who found it useful for a short time. They have also said that they were unaware of the mystery shopping forums and other sources for jobs. Most either have not gone that route, or not found spending money on otherwise free information to be a good investment.
There is a list of legitimate mystery shopping companies here, on Volition.com and on the MSPA website. While legitimate does not mean perfect it is still recommended that you check out other shopper opinions on companies. Another good source to help someone new target companies is Jobslinger.com. They also have both a paid and free version. Unlike Shadow Shopper, the job postings are available with that free membership. The downside is jobs listed may be out of date. The upside, you can see exactly what companies are currently offering jobs in your area and focus on them first. I don't recommend stopping with those companies. In mystery shopping it is definitely the more the merrier and there is no such thing as registering with too many companies.
Equal rights for others does not mean fewer rights for you. It's not pie.
"I prefer someone who burns the flag and then wraps themselves up in the Constitution over someone who burns the Constitution and then wraps themselves up in the flag." -Molly Ivins
Never try to teach a pig to sing. It's a waste of your time and it really annoys the pig.