Hello Vince
As you commented is totally normal and fair that you stablish a compensation structure and furtherore that you can track his/her performance in order to pay.
As a rule of thumb the compensation structure is variable and is frequent that you pay for an action, in this case i.e. you can pay for referrals. Of course, its going to be very important that you can also establish the quality of this referral and also a quantity of money for each,
I will be more than happy to dupport you if you have more questions about or if you want my help.
Regards
Zuli