Dear Jisha,
"Recruiter on Demand" is nothing but hiring a freelancer. You are the purchaser of the services and the recruiter will be a service provider. You have the following options to avail of the services of the service provider:
a) Enter a one-time agreement. In the agreement specify the terms and conditions. These terms and conditions will remain the same irrespective of the type of recruitment assignment. While issuing the Purchase Order (PO), mention the terms and conditions specific to the assignment. However, make sure that these do not contradict the fixed terms and conditions.
b) If you do not exercise option (a) above even then also you can issue the PO that has fixed terms and conditions and specific to the assignment.
While issuing the PO, mention clearly the PO number, the procedure to raise the invoice, payment terms, conditions under which payment could be withheld either fully or partially, the timeline of the services, will there be any performance incentive etc.
Thanks,
Dinesh Divekar