Double-sided reward, or only thank the referrer?

A double-sided offer (the referrer and the new customer both get something) has been easier to explain than a referrer-only bonus. The new person has a reason to finish signup, not just click. A single-sided thank-you is simpler to operate if the reward is manual. I would only do that if the payout is something you can fulfill without arguing about who qualified. If you have run both, which one actually got shared?