After you have your dedicated email address and Paypal account, you will want to go to the Mystery Shopping Providers Association (MSPA) website and get certified. The introductory certification (silver) is sufficient to get started. MSPA also offers gold certification, but you will not need this right away. Most mystery shopping companies will ask you if you have MSPA certification. This is their way of knowing that you understand how mystery shopping works and what is required. Be sure to use your dedicated mystery shopping email address when you do your certification. When you sign up with the mystery shopping companies, they will use the combination of the certification number and the email address to verify your certification. As of this writing, the cost for the introductory certification is $25. MSPA is the ONLY organization you should pay money to as a mystery shopper. Legitimate mystery shopping companies will NOT ask you for money.
You can go here to get certified: http://www.mspa-na.org/certification