Hi,
You can have a simple referral policy wherein you can pay an amount depending on the levels you have in your company. For level 1, being the highest level, a certain fixed referral amount can be given, which your management can decide. You can pay this amount either after the confirmation of the referred employee or, say, after three months of the completion of services of the referred employee. If the referred employee leaves before confirmation, you can include a clause for the recovery of the referral amount from the salary of the employee to whom you have paid the amount. Your referral policy should mention such points clearly.
If any other information is required, feel free to write to me.
Regards,
Harshad