A recommendation letter offered by a helper's former employer is useful for evaluating the helper's previous work performance. Sometimes the helper's former or current employer is ready to talk with you about how the helper performed when working for them. Check The Importance of Domestic Helper Recommendations Unravelled for more about a recommendation.
In some of the helper profiles, you can see their previous employers have left them a recommendation. And sometimes in the Experiences section, the helpers mentioned that their old employers are contactable. You can ask these helpers to provide their employers' contact information for a reference check.