I haven't shopped with Satisfaction Services in many years, but they are legitimate. BLD scheduled for them when I worked with them. I worked with Elise, who was memorable - in a good way! There's an Official List of Mystery Shopping Companies at the bottom of this page. You can check it to make sure the info you're receiving is from the actual company.
I'm assuming whatever you received from them was via email. If you were contacted via US Mail, it's a scam.