This investigation is out of Chicago, but good info:
Unit 5 posted ads seeking sitters on both Sittercity and Care.com. We then sought out four applicants who agreed to create sitter profiles on each site and then apply for our positions as part of our investigation. Once they applied, we requested background security checks on each of the four applicants.
http://www.nbcchicago.com/investigations/unit-5-babysitter-background-checks-179041071.html