Just my opinion...
I cannot imagine a situation where I'd want to pay someone money for a referral.
IMO it's not very professional. That being said I have given a bottle of nice wine to someone who has been a steady source of referrals through the years.
I've also seen another agent across the room in a restaurant and paid his bill because he CONSISTENTLY refers his health business to me.
To me it would cheapen the value of my services to pay money for referrals.