I went to a focus group a few months back and the check I was paid with had the TNS logo, as well as the name badges of the moderators. I think they have their hands in a lot more than MSing and have SWAG to promote themselves.
TNS is a HUGE marketing research company. They play with the big guys - Gallup, Neilson, Maritz. Their mystery shopping business is but a small bucket in the huge research pie.