Payment Management

In our future sites, we want to allow a user to post a service. We
will charge the customer for their listing. Our site will then allow
other users to request the service from those postings. Therefore,
the customers will pay a fee plus a service charge (we keep that).
The fee goes to the service provider. Has anyone provided such a
setup through Paypal or other payment systems? Is there a better
way? Thx.