The hallmark of a "good" referral relationship is one that has both parties feeling as if they are getting benefits.
Traditionally, that might mean that if you and I are in a committed referral relationship, then for every referral you send my way, I'd certainly send one back to you.
But this is where the real world clashes with the ideal world.
First of all, not all referrals are equal. The ten referrals I send your way, could be far outweighed by just one referral you send to me. Unit measurement is probably not the best way to quantify the results of such a referral arrangement. Measuring referrals exchanged by two people is probably better achieved by noting dollars realized.
Additionally, in strongly committed relationships, what one individual wants, may have nothing to do with a referral. This person may want a speaking engagement, an invitation to an event or even just your time. They may give business referrals in return. So the relationship is satisfying the needs of both, but the referrals are not equal.
What this all boils down to is that both parties have to talk with each other openly and honestly. Then and only then will the relationship thrive.