You will get a whole lot of different opinions about Shadow Shopper and about Certification, so read around the forum. There are threads on both topics.
I would encourage you to check out jobslinger.com which is free to sign up. Put in your zip code and the distance you are willing to travel. Look at the companies that have posted jobs in your area. These jobs will most likely not be available any more, but it will give you companies that shop your area. Sign up with these, check their job boards regularly and see if that provides you some jobs to get started. Many places post all of their jobs at once so April jobs may be all gone except those so miserable no shopper wanted them. But May jobs are beginning to post. Many other places post throughout the month so at any given time may have fresh jobs in addition to the "stales".
My personal reaction is that Shadow Shopper is not necessary if you have some minimal research skills and a little patience. And reading the threads about certification you will find that I am adamantly against it. But there are other points of view worth looking at as well since your market is not likely to be the same as mine in terms of availability of shops an shopper saturation.