Collect a non-contingent fee from families. Families are then provided the means to contact the nanny candidates directly. Families do all screening of prospective nannies. Families make all job offers. Again, there are generally referrals for tax and insurance issues on the site, as well as tools such as sample work agreements, in template format, provided to the family.
Families order the background investigation, and pay for it directly.
Families craft the final work agreement. They are responsible for making any transportation arrangements, if applicable. Compare that to the telephone ringing constantly from a newspaper ad, usually in the middle of dinner, bath time, and when you want to relax. Newspaper advertisement is the most common. Most daily and weekly papers have a category for Nanny, Childcare, or Domestic Help wanted advertisements.